Unexplained loss of framerate

Hi everybody i hope someone could explain that.My FS9 was working nice then i went abroad for about 10 days and since I came backmy FPS doesn't want to go higher than 9 to 13 fps no matter which plane i use or scenery.I got 13 fps with the cessna at the default seattle. If in external view the FPS are OK but each time i seat in the cockpit it drops.Of course this is with full traffic and almost all sliders to the right.Did not have this problem before and my comp was closed and unused since then....I checked the CPU ,RAM and graphic card with cpuz and speedfan and evrything looks fine.CPU is 6600 2.40ghz that i push to 3.40 ghz when using FS . But even without overcloking i had good FPSGC is 9800 GT4GB RAMI have both XP 32 & 64 bits and the result is the same on both OS.....Very strange i touched or changed nothing and it happened ...Any idea appreciated