Here's a checklist to return to normal and do no harm if you're inclined to be your own Doctor.  These are steps we do for ourselves and our customers preliminary to deeper troubleshooting.:

Warning - during the performance of this checklist, you should see steady progress and feel hopeful that a return-to-normal condition is coming.  If things hangup or sound funny or get slower, SHUTDOWN (you may have to hold the power button down for 5 seconds to do this).  You are being told it's time to get a full backup, deeper cleanup by a pro, and a new hard drive.

1)  Close open applications, saving your work.

2)  Order a scandisk (it'll happen as part of the next startup).

1. Double-click My Computer, and then right-click the hard disk drive you want to check.
2. Click Properties, and then click Tools.
3. In Error-checking, click Check Now, check Automatically fix file system error, and Start.

3)  Do a normal Windows Shutdown.

4)  Restart into Safe Mode - (a bit of a tricky, timing thing) depress the F8 key just before the Windows logo appears.  Multiple taps on the F8 key is OK.

5)  From bit.ly/1pfQuTg download, install/run cCleaner to purge junk files. (always a good thing to do weekly)

6)  Perform a full virus scan.  Repeat until nothing found.

7)  Perform a Malwarebytes Anti-Malware scan.  Repeat until nothing found.

8)  Do a normal Windows restart.

9)  Get up to date using Microsoft Update.

At this point, if you're happy and relieved, now's a good time to start a backup plan like Mozy.

If no joy, it's time to call a pro for further backup and cleanup action.