|I'd delete everything in the c:\windows\prefetch folder (safe - it's just used for boot caching)|
Clear your Internet history/cache.
Run chkdsk c: /f to fix any lost file chains (you'll hafta reboot since the C: drive is locked)
Run defrag /f (to force it to run if space is too low, just a habit)
Standard hard drive cleanup - delays when double-clicking are generally related to seek issues because the files are fragmented across multiple sectors or confused.