My n900 is refusing to start.wen I press the power button nokia comes on the screen and the blue light glows but after about 20sec the device switches off.pls pls help.

More information regarding other things you have done might help. Which charger are you using--USB or wall? What happens when you connect to a computer. Etc.....

This usually means the battery is too low.

When I connect to a computer a very dim light comes with nokia written.I use wall charger which came along with my mobile.also I tried a fully charged 5800 battery but the problem remain

Hey friend, Try taking out the battery and use an external charger for 6 hours . Press power key for 10 seconds before inserting the battery. Then try to switch it on. If nothing, probably you need to reflash. Do you have Kernel installed?

I tried to flash but my computer is not detectingg
The phone.mate pls help and thanks for ur speedy reply.also I am a newbee in linux and dont know what are kernels

Try doind as I said, charge the battery on an external charger for 5 or 6 hours before reflashing. Google for 'tablets dev n900 page' download the correct image for ur device download and install maemo flasher 3.5 put the image in the same folder of maemo flasher. Under windows it is on C\Program files\maemo . Then run the comand flasher-3.5 -F RX-51_2009SE_20.2010.36-2.002_PR_COMBINED_002_ARM.bin -f -R
Replace RX-51_2009SE_20.2010.36-2.002_PR_COMBINED_002_ with ur correct file or leave like this if it is the same. If you still can't let me know then I try to post a small tutorial, but let me know wich PC and OS are you using and N900 FW version. And press Thanks! if I've helped you.

thanks now its working thanks a lot

I am glad I've helped you, my N900 was dead for 10 days aswell, that is why now I know how to do it, am new with this too, since September and am loving, even with some problems like you had, we just need to be careful with what we install. You forgot to click on Thanks! !!!