I have tower PC running XP with MS-7207 MB, upgraded Corsair PS, and Daimond Radeon HD3850 video card. Recently the card disappeard from device manager. I switched to integrated nvidia to get by. The Radeon "reappeared" two different times, but again disappeared on subsequent restart. The PC had been running > 1year with video card prior to this happening. Is this a failing video card? Motherboard? Power supply? Something else? Thanks.