Is my graphics card defective?

I have an Nvidia GeForce 9800 GT, and ever since i installed an update for it, all of my games were under 10 fps. even when i removed the update and went back to the previous version, the lag remained for all my games. I was able to run Call of duty: Modern warfare 2 at a good 60-70 fps on max settings and now even on the lowest settings it lags. This occurs with all my games that i have. Should i re-format my computer. (Currently using windows 7 64-bit) Or should i take it to a computer store to get it checked out. Any more suggestions on what I could do?