Is your Zone Alarm a recent version? I actually just had issues with Zone Alarm on my home computer and removed it, and my system boots up twice as fast now, and programs load faster. I'm temporarily using the Windows firewall until I can figure out what the Zone Alarm issue was or else find a suitable substitute program.
As long as you have the Zone Alarm installation file handy, you might want to try temporarily uninstalling Zone Alarm to see if that makes a difference. If it doesn't, you can then reinstall it.
Also check your paging file size. Goto control panel/system/advanced/performance/settings/advanced/virtual memory/change.
See what's listed there. Is the minimum paging file size larger than the listed recommended size? If not, make it larger (go up a half gig or so over the recommended) and see if that makes a difference.
PS -- don't do the paging file thing if you don't feel comfortable navigating there.