the video card before was a sapphire radeon 9800xt, and i used drivercleaner before installing the new drivers. this new card (HIS Excalibur ATI Radeon 9550 256MB) is still giving me the problems. i've got the 6.7 catalysts installed (also tried the omega drivers, but they're based on 6.5). sometimes when the screen goes off if i wait 20-30 seconds it eventually comes back on, sometimes after a nice display of red/green/black gibberish all over the screen. other times it will just freeze up completely and a reboot is the only way to get back on. i had a search around and other people have had the same problem with this card, someone suggested it may be due to games which use hardware acceleration (that's usually when it goes mad, while playing games. WoW mostly) although when i tried to use MP3Gain it also crashed it, so that made me think it was something else. all other applications seem to run fine but i cant open mp3gain without it freezing up. following up on the hardware acceleration thing, someone on a different forum asked about it but never got a reply. so i dont know whether to send it back and get a replacement, send it back and get an equally cheap nvidia card (i dont want a brand new card until next year when i plan to upgrade the whole machine) or just grin and bear it. sometimes it can freeze every 5 mins, whereas yesterday it froze up twice.
oh and i did use the compressed air on the power supply before i fitted the new card, cleaned the whole inside of the PC out. and on the occasions when it does come back after freezing, the keyboard lights do work (when pressing caps/scroll lock) and if i hold the key down like suggested when it has completely frozen nothing happens. if the speakers are on at the time i get a repeat of a few clicks or noises until i reset it.
edit: it's just completely frozen while i was doing nothing, so maybe it isnt games only causing it. and i managed to write down some of the error messages i've had so far.
STOP 0x000000EA THREAD_STUCK_IN_DEVICE_DRIVER
and
STOP: 0x100000EA THREAD_STUCK_IN_DEVICE_DRIVER_M