IE, Firefox, Chrome--all the same.  Have a Dell desktop maybe 8 yrs old.  Norton protection.  Windows XP and MS Office suite.  All programs and everything works fine except browsers.
  Had a couple of 250 Gb RAID hard drives when new.  One quit about a month ago, the other picked everything up and kept on truckin' just fine.  Replaced the first with a 500 Gb, then after it was up and running, replaced the other and doubled the RAM to 8 Gb or so.  Drives are maybe 25% full with lots of photos and photo software.  All was well.

  IE is what I use pretty much all the time.  Started slowing, then slower, and slower over a couple weeks.  Found MS Fix-it, and used CCleaner.  Nothing unusual and no real difference.  Tried Firefox, which worked for a couple days, then slower, and slower.  Same with Chrome, but it never ran well. 

  Firefox may give a hint:  As it sits and tries to pull up a page, the lower left corner says what it's waiting for and it always says it's waiting to load some sort of advertising.  The actual ad varies, but always ads.  I have popup blocker on IE, not sure on FireFox. 

  I disabled every app on IE, no difference except videos wouldn't load anymore.  No java.  I have enabled some of those again.

  Norton finds an occassional virus, last one was trojan.maljavagen10 and claims it's gone. 

I'm slowly going nuts on this one.  OBTW, this site always loads and plays fine.  So does Lucianne dot com, the wall st journal site, theoildrum, theautomaticearth and some other sites.  However, ones like drudgereport, hotair, ml-implode, zerohedge, globaleconomicanalysis.blogspot and itulip take forever, if they load at all.  Other sites, it's just random--some work, some lock up.
  Slow loadings usually end up with IE just locking up, and it takes it 5 minutes to back out and end the session, with Norton giving a warning that the chips are spooling up at 98% or so while it's trying to unwind itself.

  So, great little computer, all works well EXCEPT the browsers. 
  I'm convinced it's not my ISP or my Netgear router.  My wife has a similar Dell setup working off the same router, a year newer and all those functions work just fine.  I have a 3 MbS ISP and it'll test about that most all the time.  I've used a cable direct from the router to the computer (no wireless) and that makes no difference.

Any ideas welcomed.  Thanks a million.  Stetts