Windows 7: ATI Radeon Mobility HD 3470 - TOSHIBA A300-15K

Hi
I've just installed Win 7 on Toshiba A300-15K. Everything seems to work fine besides graphic card. I installed drivers from Toshiba site, but it keeps reverting to 1024x768 resolution. I mean it's pretty random. Every once in a while (30-50% cases) system starts up and has this low resolution and touchpad and keyboard is not working.
(in device manager radeon comes with (!) sign and it says there are some errors - don't remember - it's in polish)
Only mouse is working, so I can shut it down and start again. Then it comes up with native 1280x800... (and no problem in device manager)

I've tried already installing modded drivers (modder.net) but it says I have latest version of drivers and won't install

What could be the problem ?