FPS dropped from 40 to 8

All of a sudden in the last two days, my FPS, which is usually around 40 FPS, has been down under 15, as low as 7 FPS.

It's like a slideshow- there are even bursts where I'm typing faster than SL can apparently render the letters, and keys actually get missed when the text finally shows up.

Watching my system resources, it's taking 100% of both cores when I run the software. Generally it only takes 75% of each, tops.

As far as I know, I haven't done anything different or changed anything.

System specs-
CPU: AMD Athlon (2999 MHz)
Memory: 3071 MB
OS Version: Microsoft Windows Vista Service Pack 2 (Build 6002)
Graphics Card Vendor: NVIDIA Corporation
Graphics Card: GeForce 9800 GT/PCI/SSE2/3DNOW!
Windows Graphics Driver Version: 8.15.0011.9038
OpenGL Version: 3.1.0

one of two problems i can think of. your internet is fubbered contact your ISP or you have "invisible" backround processes running. if you using windows press ctrl alt delete then go to processes anything using over say 20-30k+ that you know you dont need end the process be CAREFUL though never end system processes or processes you dont know what they are because you can permanently screw up your computer. uusually its pretty simple to figure out what they are like firefox is firefox.exe your main "operating system" process is called explorer.exe (i wouldnt suggest ending this even though i occasionally do if you do just make sure you start it back) if you using windows xp. also sometimes your computer is wrong due to lag or other issues my system % usage sometimes jumps around like a madman simply restart your computer that usually "refreshes" things.