Why do I have to reinstall sometimes due to running slow?

My new laptop runs SL well but lately sometimes when I log on I get much lower fps then usual. I've tried everything to get them better, but the only way to get them back to normal is to uninstall the viewer and reinstall it. Is there another way around this?
My laptopis an ASUS with intel Duo T5550, 3 gigs memory, nvida graphics card 9500m with 512M, if that info is helpful.

Have you tried either clearing cache (from Edit / Preferences / Network) or deleting just the cache files themselves, short of actually uninstalling? (This is just kind of a hunch... usually clearing cache is for when the contents are corrupted, but it is one side-effect of uninstalling that might possibly affect performance.)

I tried that but clearing cache didn't get my fps back up to normal.