Why is my puter crawling?

I've tried folks! I've defragged, I've cleaned up C drive/disc (whatever). I've deleted programs I don't use. I've recently put in a new modem.

I have no idea why I'm all of a sudden taking much more time to load pages. It could be anything from downloading a pic at DG to opening a web search page. (I find myself staring at the little "horizontal graph bar", watching it creep along...sometimes only to end in a "Can't find page, refresh, blah blah blah...")

I used to connect at 38 or more (dial up). Now I connect at 32 but can't believe that difference would bring up this much trouble. I also never used to have trouble with MSN Instant Messenger (I get bumped off it quite often)...never used to (however, recently I DL'd the newest version, something to that maybe?). I've tried "repairing" that version, but to no avail. If I get rid of it, how can I get the previous version back?

Surely there must be some way to speed this system back up again. Any idea of some things to check next? Please? Pretty please!?