Opening Programs Takes Lots Of Time?

it enters a kind of loading spasm which can go on for several minutes, making this repeating, rhythmic pattern of loading noises, before everything goes back to normal. Foxit Reader and McAfee Security Center are the worst, but right after booting most programs cause it, as does merely logging on which now takes about ten minutes. It doesn't exactly make the computer unusable but it's incredibly frustrating. Outside of the spasms it's perfectly normal.

I haven't installed anything recently, except for a demo of Penumbra: Black Plague which I've since uninstalled . I have very little free hard disk space (1.5 GB of a 60 GB disk) but that's been the case for some time, while this only began a few days ago. I've done full scans with Ad-Aware, Spybot and McAfee which turned up nothing more than a few tracking cookies. I'll paste a HijackThis log if someone reckons it'd be of use, but I'm uncertain whether this is a malware problem (hence my not posting this in the malware section). It's occurred to me to just format and reinstall windows, but perhaps there's a likely simpler solution?