I ran Malwarebytes from my flashdrive and my AV quarantined it as a virus. I then disabled my AV and downloaded Malwarebytes to my hard drive and ran it. No malware was found. I checked it with several other antimalware programs and came up with the same result.
I then restored my hard drive to its two-day prior configuration and now my Win7 system works fine. At the time the problem occurred, I was simultaneously running the Google Chrome browser from my flashdrive and IE9 and GreenBrowser (which uses Internet Explorer as a proxy) from my hard drive. Could that have caused a conflict?
Anyway, thanks everyone for your input. I have since checked my system with several remote AV scanners and no viruses were found. There were about 1,200 junk and cache files found by A1 Cleaner that I deleted, which CCleaner did not find.