So I'm not the only one
I was stupid enough to touch my rock solid XPMCE install in the bedroom and install SP3.
Had the exact same problem and I had to restore to a previous time, however don't think it rolled back completly clean. I have tried it twice now.
I used the free Microsoft on line support. An e-mail was sent to me giving me a number and that someone will come back to me. They were nice enough to have a survey company send me an e-mail a few days later, asking if I was satisfied with their response now that my problem had been resolved. Naturally I didn't get a response so my survey remarks were rather negative
I've resigned to the fact that I will stay with SP2.
My Mobo is a DG956OT, see my second rig below.