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.