Oblivion played perfectly last night. Today it does not. As soon as I start the CD, even before loading a game, scratchy static sounds intermittently come from the speakers. The game loads as usual and "plays," but the frame rate has declined (from 60-70 down to 8-20) and the occasional static sounds continue. Does anyone have an idea what may have happened and how to fix it?

It may not be the A-Bomb. Doors open normally (I tried a few in the mages guild) and the flames in the Cheydinhal street lamps seem unchanged. Also, I have read that the Bomb usually occurs after 200 hours of play and this game has 140.

Occasionally the game returns to normal for a few seconds, then reverts to the problem. Between last night and today I changed no settings, added no mods, nor did anything else I can imagine causing the problem. The computer acts normally when I'm not playing Oblivion.

What happened?

(I tried the game disk in another machine. It worked fine, so apparently the CD is not the problem.)