hmm i can guess that u take ur n900 to gym by looking at ur todo list , if u put it with ur sweaty clothes or humid place u will affect the phone.

solution : open it remove the battery and point a hair dryer all over it , be careful not to melt ur phone , do this for few minutes till it dries .

ps: mine had the same problem and the cause was the gym ...

Same problem, same solution.
Screen protector removed and no more touch screen problems.
Thanks by the idea !

same here, suddenly no touchscreen response, can only login as root with x-terminal or backup menu.

didn't drop it, no special humidity, just went from 5 degree C. outside, to 20 degree inside. maybe condensation, corrosion etc.
tried to dry it with a fan, no result. removed screen protector.
just a few weeks after the warranty expired.

how do i read out the status of the touchscreen device? it seems to receive no input. how to reset factory settings from terminal? or initiate the touchscreen calibration routine?

any chances to get it still fixed? cannot say that i didn't have trouble with this phone before, but despite the usual hickups, the touchscreen never just went completly off before.

Facing the same problem and taking same solution. I'm waiting for a week for an answer from Nokia Care Centre in my city. They're suposed to be looking for a screen digitizer somewhere among Spanish Nokia Care centres. If not replaceble, they give me a Nokia E7 for free. LOL. I don't want that stuff. It will be my last Nokia for sure too. More than angry!

the screen problem has got me too. I couldn't point the true reason for it to happen, but i'll try the solutions here. Just to contextualize e see if anyone is having the same issue, here's what have happened and how the phone is behaving: the day befores yesterday it fell from my pocket while i was trying to take it out. It showed no problem at all, worked perfectly. then i went to sleep and in the morning screen didn't respond. I reflashed it and now i'm stucked in the time and place settings screen, but now instead of not working, the screen is erratic. touches work as swipes and sometimes it doesn't work at all. but i think the screen recognizes the presses, since when i touch the physical keyboard lights up.
weird stuff.

It's back to normal. I don't know how, I don't know why, but it's working properly again. That's it.

This thing inside of digitizer makes it stop responding..I think it's moisture. Leaving my digitizer in a bowl of rice for one and a half day,exposed to sunlight, brought it back to life.



PS.
It's impossible to see this spot until you disassemble it.

Same problem all around. Replaced the digitizer completely to no avail, reflashed the whole thing, put it in rice, performed magic rituals.

Nothing.

let me start by saying that i know all the possible solutions for this problem and will get into those one by one.
But i just wanna start by saying that I'm very disappointed with people using N900.so a teeny tiny problem and N900 is not a good phone anymore huh?AND,to add to the misery,people commenting and posting answers don't know a thing which makes it extremely hard for a new user.people post answers like 'reflash it' or 'take it to nokia care'..For God sakes!
now,the best solution for any problem is IF you know the problem.what i did was,to one by one try out different things that might cause my nokia N900's touch system to go haywire.i found four interesting things.First,the protective cover caused this problem every single time so don't use them.Second,don't install nokia kernel for advanced user if you don't know how to use it.there are other softwares too which caused the touchscreen problems for me.Third,drastic temperature changes cause this problem.for example if you keep the phone right under the AC for a whole night,or keep it under immense heat like direct sunlight.Also,moister from the hands or sweat caused it for me so beware.Fourth and most important,always use N900's original charger to charge the battery.It was surprising for me to see that my nokia's touchscreen developed problems after i charged it with another charger for three nights on a trot.
lets talk about the solutions for all these problems.For first,you just remove the protective cover and the touchscreen will be fine in at most a couple of days.For the second one,be careful that you install only the softwares that you really need,and uninstall the recent ones if you have this problem.For the third problem,give your N900 the optimal temperature and handle it with care and love,and it will be fixed.If there's water or moisture problem,just turn off your N900 and give it two to three days to dry out and then turn it on.For the fourth problem,start charging with the original charger and the phone will be fixed in a couple of charges.By the way,always let the battery drain out as much as possible,let it turn off by finishing off the battery charge if possible,and charge it fully everytime you charge it.
I'm pretty confident that one of these WILL fix the problem as long as its not a hardware problem.The hardware problems include the bad ones like a broken lcd,or a relatively cheaper one like the touch ribbon under the lcd might be displaced or may be the whole touch system has gone bad.The solution for a damaged lcd is to get a new one,the solution for a displaced touchscreen ribbon is to adjust it,and the solution for a 'gone bad' touch system is to change the touch system which also comes pretty cheap.
i absolutely know for sure that this answer WILL help atleast 95 percent of people here.no need to reflash your N900s anymore,there're much easier and simpler solutions available.N900 is undoubtedy the most intersting mobile device that i've used,and i love it to death.Thats why i couldn't just sit back and see people saying bad things about it,and others answering badly and being no help at all.
I'ld like to know what my comment did,how many readers it helped with their problem,and if there're anymore problems,just let me know somehow.i'm always around and would love to make your N900 experience as cheerful as mine.cheers mates.

I was Having a problem with the touchscreen. After a being away for so long I decided to buy a new N900, as my old N900 lost it's usb port about an year ago, and i'm not skilled enough to repair it myself. New phone arrived month ago. Soon after I started having problems.

So I had this annoying little problem that left side of the screen wouldn't register touch or would register it to more right than it should've been. First I thought it was caused by humidity as I keep my phone in my pocket while working and sweating. I tried to dry my phone with hairdryer and it worked. Eventually the problem came back worse and I realized that the problem wasn't caused by moisture. Whole touchscreen was dead. And then I tried blowing between the screen lid and phone. It did the trick so I could use my phone most of the times.

Finally after a week I got tired of my phones tricks.I plucked up courage and started to disassemble my phone. I had a hunch that the touchscreen cable was the culprit and so it was. After disassembling the screen assembly the cable just dropped off. Now after cleaning and reattaching cable the phone is working like a dream.

http://www.youtube.com/watch?v=pDQ81cahD1c
This video helped a lot.

I hope this is a helpful info to someone.