PC "Not Responding" - Blue Spinning Circle?

I've been all over the internet looking at how to resolve intermittent (every 2-3 minutes) slow responses on my Acer laptop that I've had for over a year. 4 weeks ago I had no problems with it. Since then, the internet window I'm on freezes, goes white and says "not responding". I thought it was Firefox at first so I uninstalled but it's the same with Chrome and IE too.Equally if I browse photos, they take forever to load.I hadn't installed anything new or updated anything when the problem occurred so I have done the following to try and resolve (all found on the internet)... Checked the processes running... max cpu 1%... memory 30% - nothing out of the ordinary at all Rolled back to the previous system restore point - no joy Updated my Intel graphics drivers Checked that there were no issues in device manager Run check disk and other tools to confirm drive is sound (it is) Defragged the drive Done a virus scan and spyware scan Run several regfix tools that allegedly speed up your computer (free and purchased) Reinstalled firefox and set max network connections to 42 (from 255) Stopped everything from starting up in MSConfig (eg spyware and virus checkers, adobe etc etc etc) Searched and removed a particular string in the registry (though I cannot remember what that was - sorry - but it did make sense at the time) Alas nothing seems to work. I have seen reports of this all over and have tried everything I can find. The only thing I haven't done that has been suggested is an install/repair as I haven't the disk to do it with (the OS is OEM on the drive and you can only do a full restore which is a last resort).