Thanks for all those thoughts,

I think the chargers were the problem:
a few weeks ago, I ordered a USB external battery (you put a 18650 lithium battery in and it does the job), curious, I tested how the N900 would charge on this device, and I connected a USB cable, the phone charged from low battery to full battery in a matter of 2 hours (I don't know if it's normal), this evening:
I'll use the device and save my data (to see how long the battery will hold charge)
-change the keyboard and check everything
for now: I'm charging the external battery now

and tomorrow I'll reflash the N900

I'll also look for an original Nokia charger once I'm sure that the chargers were the problem

on my main PC, I use Debian Linux Jessie AMD64 but I have a working Dell Laptop with windows XP Pro. on it if it's necessary/prefferable.

@endersormeans: ok, I'm preparing the reflash
@jellyroll: Because
-I saw a lot of stuff people made out of it (like a SDR receiver device, playing SNES, CPC, ... emulators on it, ...),
-I didn't wanted to buy an Android nor a Iphon and my old player light is getting a bit outdated
-I liked the idea of a resistive LCD and a real keyboard (even though it's not the best keyboard ever)
-it runs a Debian based OS which seems cool
-the phone is COOL because it's not like the other phones
-IDK, it's just an awesome machine

@endersormeans: it seems that I won't have to do any hack (I was thinking of taking the outputs of the battery and adding a dc jack connector to the side of the N900 so that I could plug a TP4056 charger to it

"I was thinking of taking the outputs of the battery and adding a dc jack connector to the side of the N900 so that I could plug a TP4056 charger to it "
Interesting possibility....
I would suggest doing such a thing to a n900 which you are willing to experiment with...
I'm keen to see the result if ever you play with such an idea...

and yeah... best to use proper chargers ....until you have extra devices to mess with...that is ....


remem. though...
the nokia software updater is fabulous for n8x0's.
when using the nokia software updater , an n900 and windows...
it really can only do the firmware at best.
more than that it cannot do.

afterward I would suggest doing proper setup via linux.

ok, I'm finishing to save and I hope tomorrow I'll be able to flash the thing (I guess there are plenty of tutorials on the subject )

on maemo-repos.com
http://maemo-repos.com (highly suggest you reallllllly look over everything there...ie. properly set up your repos from there...it's located at the bottom of the page...easy catalogue setup too...)
http://maemo-repos.com/apt-mirror/custom-emmc/
there is a section with 5gb emmc I believe...
this I would advise to flash....
what I have on all my n900's...
basically it expands the stock onboard partition up to 5gb for more applications taking from the overall storage...meaning instead of 27gb of onboard storage you end up with 22gb for storage...small sacrifice.
there are other versions with greater or lesser (including the stock flash) space for installed apps...but I think the 5gb option is a good sweet spot.

It seems to be quite popular but personally I have never found the need. The default allocation on the N900 is as follows:
27GB for data
2GB for applications and settings
768MB for swap
64MB unallocated

That unallocated bit bothered me, even though it is peanuts, so I shuffled my partitions around, extending the second partition and moving the swap up. So I have now 2.06GB for apps and settings. And guess what? In two years I've had it like that, I never filled it up to more than about 55%.

After 5 years (one reflash in 2010 due to dumbness as did not take fcam drivers from extras-devel ) I have now filled it up.
Only 15 MB on rootfs and around 100-150 MB on optfs. HAM refuses to install/upgrade but terminal/apt-get work reliably to me!

So it is matter of taste.
I'd prefer a 3G optfs, but iirc one can hexedit the image file.

I didn't have time today either, I'll do it tomorrow (I have finished to save, the charging problem is gone since I removed the Nokia for power users kernel thing and a bit of other stuff)
Thanks for your answers, I'll see for the partition setup but expanding the Application partition seems a good idea .

Didn't have time this week end, I'll do it wednesday ,
save OK
W$ XP PC OK

Hi,
I think I'll need your help here, I tried to find what I thought that might be of interest but I didn't find good sources for the Nokia tool and the image for Maemo, also I'm hesitant about whether I have to make a soft reset or a hard reset, can you help me on that (I have finished to save the things I got on the phone but I did not get anywhere further)

Thanks in advance

PS: Sorry to have been absent these days but I had a bit of work

After quite a bit of time not being there (because of exams), I have finally made the flashing, there is no custom kernel or bootloader anymore, though in the time of me not being there I had a little problem that was not fixed by the reset (it removed all the install software though contacts and messages are still there and on the first boot the wallpapers were too)

so the problem is that I dant communicate over the GSM network (or any 2/3G technologies for that matter), this is a big issue for someone like me who wants to use his N900 as a phone :P

do you know what I should do about that ( I read that it might be software related or might require another board/some tinkering with tape on the sim)

though for the tape I'm not convinced as I also get the error when there is no sim card in the phone.

here is the error:
All telephony functions, including emergency calls, are disabled due to a communication error. To recover, you might have to reboot the device.

I already had this error popping sometimes, just before I stopped using the phone because of it, in march or april but now it's always

Thanks in advance for any tips/helps

ps: From what I saw that the flasher is not free software nor open source, is it ? and the licences regarding the images and flashers were weird, I will have another look someday, that's odd from Nokia to have acted in such way...

Did you do a power search with above key words?

There are dozens of threads handling this topic.
Some claim thd paper trick (only for a few days) , other the oven trick (did not try). I posted something to disable that annoying pop up.

tldr
your modem connection to the board is broken, GSM functionality dead