I managed to wreck my touchscreen on the 5800XM by pressing down on it too hard. It was a similar situation of me applying a screen over it and I guess I applied pressude pretty evenly throughout the surface of the device with same result. My touchscreen would work from time to time, but sometimes an icon in a certain place on the screen would get pressed by itself.

Took it into a Nokia Care point, it took them less than 24hrs to replace the screen with no cost to me. Naturally they also cleared out any and all dust under my screen.

Thanks cjp...its a relief to hear about it..thing is i purchased my phone from saudi arabia....and currently I stay in india and Iam unsure if the n 900 has been released here ...and if the spares would be ....anyways Iam gonna check it out....

i was playing football, with my n900 in my pocket
it was raining, and when i tackled, the n900 went all wet! i let it open till the match was over, and when i got my phone back, everything was working besides the touchscreen.
i closed and opened it for 100 times and nothing happened...then i got home, and i blew some COLD air from my head-drier and put the battery back in....the result was the same...after that i put the charger on, and i opened my n900...i closed it, and when i opened it again, everything was working properly (the only thing not working right is the backlight...it stays on forever, and i cant reduce it)
try it