I've got a 2010 Dell Studio laptop, Intel processor, 4GB ram, 320 GM hard drive (180 GB consumed)  running Win 7 and IE 11 that is giving me CPU usage problems.  I don't know what all is related so here's the story.

I was experiencing slowing of my download speed - dropped in half every 2 hours or so after a restart.  Occasional problems with computer speed as well and when I checked Resource Monitor I would see CPU usage bumping 100%.  A restart always fixed the problem.  Running in Safe Mode eliminated the loss of download speed so I knew it wasn't a problem with hardware or my cable modem or wireless router.  I explored a lot of possible issues but none resolved the problem so I reinstalled Win 7 on Friday, January 16.  Download speed not only fixed but faster than it was before.  It remains steady and doesn't decay so there was something wrong with the OS, etc.

However the CPU usage problem remains.  What seems to happen is that something triggers high demand and then every process on the computer joins in.   When I look at resource monitor right now it's consuming 1.3% of CPU but when things are choking it is consuming 15% of CPU, and all the running processes jump from like 0.5% to 5%.  So you can't point to a single process as the culprit though it's possible that high demand web sites (lots of ads) trigger the problem.  I'm going to do some research on that.

I've done a lot of web searching as well as this forum and none of the fixes seem to either work or apply to me.  I've run a Malwarebytes scan and a full virus scan with Microsoft Security Essentials: nothing found.

The computer is almost 4 years old but I would hate to spend the $$ to replace it and find that the problem is software.  Any ideas?