Thanks,
I hope I will reach the goal, are the 20$ lcd from china good ?

Anyway, thanks guys for the support, I think that made a good replacement for my today episodes planing from "Malcolm" and "Game of Thrones"
So now I should go for a new lcd and usb but I'm wondering about these bugs and reboots, Is it possible to fix all the software problems before the hardware ?

But I don't have any usb port (the µUSB is out and I don't even have it), Is it possible to flash from sd while waiting for the parts.

The battery seems to be kind of damaged too:
Yesterday it was at 4v now it's at 3.28v
So:
-LCD replacement 15$
-(New Front glass/digitizer maybe) 10$
-New battery
-New clock battery maybe
-New USB

So I'll have a lot of work these next weeks

yeah...
that usb ...forgot about that.
yeah if the usb is pooched...that will be a small task.
Are you certain that the microusb port is toaster strudel?
that is the big question.
you have tried to connect via different pc's ...
and / or different os's with it WHILE you had the monitor hooked up so you could see the results with your own eyes to verify that the micro usb port is smurfed ...right?
Otherwise triple check...quadruple check ...
if nothing is wrong ...for certain...then that is a tragic waste of labour and sweat to simply replace a possibly perfectly fine micro usb port.
Never take the word of the last owner as gospel.
For all we and you know... it is the operating system on device which started coughing up problems for the port. And troubleshooting with a good usb to micro usb cable and a few os's ...and possibly on device os re-installation may solve that...never know.
But if someone didn't take good care of the device ...then anything is possible.

I believe the OP said the port itself is gone. This will require some soldering work before any reflashing.

Having said that, my N900 has been running for the past 5 years on hot-swapped batteries due to a faulty port, and I haven't been in a position where it's needed flashing. (If it's not broken, etc.)

It is to be seen if you need a new battery and you can live without the clock backup battery. Still, 3 out of 5 plus a lot of work with uncertain results (soldering the USB port when the pads are pooped)... Unless you like a challenge and/or have a lot of experience, it might be easier to cut your losses (it's only 10€ after all) and look around for another one in a better condition. You can still keep this one for parts.

ooh. yeah..right..no port at all.
Yeah pichlo is right ...you gotta be pretty decent with a soldering iron to do it right.
hm...
and yeah...it is unknown damage to the device.
You could spend alot of time and money ...
do everything right and there could be hidden probs you can't see.
and yeah ...
10 euros for even a n900 for parts is a very good deal.

Well, I tested the device with my wonderful LG© CRT TV,
it works well, I watched the answers on the topic with it, kind of better than my 2G feature-phone with shitty softs, a lot of good softs on it like an emulator and Marble, no lag, some Pr0n images on it , maybe my poor buddy was a "fap-phone" for a moment

I tried the camera but it didn't work (blueish black tint but no image), then I tried taking a photo but it said me that there was no room for other photos (with more than 30GB free)

To answer your answers, I'm definitely going to try repairing this guy, but I don't think I'll will use the original µUSB but I will make the mod with the real USB port, a lot more useful, so first, I check what is dead and what is not, then I'll reflash everything with some wires inside, at that time I will have received the new µUSB, that I'll solder with hot air and solder paste I think finally if everything is good, New LCD and when I'll have some money to throw away:
New digitizer, screen protector and housing.

No room may indicate the camera is set up to store pictures on the SD card. Or it can mean that the main file system is corrupt. That should be easy to find out. There are many cures for a corrupt file system; most of them involving the USB port (that you don't have) but some not.

If you manage to get your new toy online, there may be some chance even without reflashing. That way you can live without the USB port, provided you can charge the battery elsewhere. I know of a few people here who use it like that, one even replied in this thread. I myself use the USB port only for charging, everything else can be done y WiFi or Bluetooth.

Then your only remaining problem is the display. That is not that difficult, although I have been lucky with mine and never had to use the cheap Chinese ones from eBay and cannot vouch for their quality.

The usb is going to be vital for me, large USB, so I'm going to mod my phone a bit, though, i'll try to put a new µUSB, a reinforced one this time, just for charging, I'll search for the pin I'm missing and make a brige-wire trough one of the test pins, I belive there is at least one pin that is 5VDC