Very sorry if I've missed something obvious but I've spent ages looking around and tried as many fixes as I could see. My dxdiag file as below (32bit version - let me know if the 64 bit is required)

Can't find a free program to log the GPU temp (suggetions welcome).

CPU temp log shows absolute worst case of 45 deg C (which seems pretty low to me).

Alternate dx3d9 dll (web suggested this was no longer required after patch 1.2) now removed.

Alternate direct input dll in game directory.

Played windowed (which was rubbish and still crashed).

multithread and AI fixes into the ini files (steam and my games folders), now reverted to original.

What I've tried (all of which have had no effect). I've spent about 6 hours searching and trying vartious fixes and am now fed up.

Realtec HD audio - latest driver R267 (6.) CTRL ALT DEL has no effect only a power off has any effect.

The screen goes black and the sound locks into a buzzing noise. The game crashes after 10 to 15 mins of game play. Bought Fallout NV ultimate addition from steam.

Fallout 1 steam black screen