COF Failure report. HELP

Had Win-XP failure after changing video drivers. Got blue screen and windows shut down. When I got computer back from the shop and up and running I now have problem after closing COF. Had to re-install win-xp updates , sp1 , all Drivers, etc. COF loads okay and while flying COF, all is okay. With or without using FS NAV and ActiveSky2004. All works fine, save flight and exit ok. When I close COF it generates an error report. The error heading is multiplayer.Dll...when I start COF again, all my settings are back down to the defalt ones. I have tried uninstalling and reinstalling COF, even deleted COF and installed it. No luck. Microsoft no responce. Have 2 HDs, Win-xp on C: with COF on D:. Do I have a hardware problem? or Win-XP problem? Would anyone have a clue.ECS K7S5A MBAMD Athlon XP 2100+1 GiG ramNvidia FX5600audigy 5.1 soundC:40 gig HDD:80 gig HDWin-XP