EVGA GTX 560

Hey guys

I am having a few problems with my EVGA Gtx 560, I installed it roughly 4 hours ago and I was happy ( my first decent rig ). I jumped onto my favorite games, MW2 I maxed it out and boom 120 - 160 FPS I was really pleased with the graphics card then I went on Cod4 and played for a bit on roughly 150 fps maxed out.

I went off and had dinner, I arrived back and quickly jumped back onto Cod4 my fps went down to 50 FPS so I am thinking maybe a lag spike, I turned down my settings and it went up to 70 I was still wondering why it went up only 20 fps when it went from maxium to lower then lowest ( Fps Config ). I got off cod4 because of that and decided to go back to MW2 about 25 minutes ago I had only 70 FPS maxed out, so my fps was bascially halfed I was a bit annoyed so I decided to post on here for some help.

I got the card from a shop 40 mins away via car, I also purchased a faulty AMD FX 4100 CPU from their today so im stuck with an Athlon Dual core. I don't think it was the dealer but its rather the card, I havn't touched any overclocking but I opened up MSI Afterburner and the maxed temp was 59 degrees.

Is there anything that can fix this issue without overclocking because if I had 150 fps drop to 50 fps randomly I don't want to overclock it to make up the 100 fps I should be receiving.