Last time I formatted my PC was more than 3 years ago, but my Windows XP still boots up in less than 26 seconds. So, not having formatted in a while doesn't always have to be the culprit of a machine that's slowed down to a crawl.

The first thing you should do the troubleshoot slow loading times is to press Ctrl-Alt-Del and take a look at the amount of running processes in Task Manager. My bet is that AT LEAST half of what you have running there is NOT necessary for your everyday tasks.

Just for reference, after a fresh bootup, I have a mere 11-12 processes active, all of which are basically the bare essentials (explorer.exe, two instances of svchost.exe, lsass.exe and a few others).