|If you're anything like me you've already solved this problem but I figured I'd give it a go. |
First, what changes have you made to your PC since last month? If none, no new programs, no updates, etc. then the most logical culprit is likely malware.
Even with an antivirus or Internet security suite running on your PC you can still be infected. A lot of these programs (McAffe, Norton) are compromised by malware so they are useless to you when it comes time to fight it.
When fighting malware I find it's best to scan a PC with tools that weren't already installed on the computer when it went south. "Portable" versions of great tools make this particularly convenient. However you can do well installing and running the following:
To kick things off try running the following:
Kaspersky AVP tool. You can get it here: http://devbuilds.kaspersky-labs.com...
Once that's done doing it's thing download and run Malware Bytes: http://www.download.com/Malwarebyte...
Regarding both of the above tools. It is best to set the scan level to high or deep and may be necessary to boot into Safe Mode. After these two programs work there is usually no need for additional tools but for good measure you can also run the free version of SuperAntiSpyware.
It's possible that the hardware in your PC is going too - a bad hard drive could really slow things down for example - but my experience tells me that a good malware fight should solve the problem.
Let us know how it turns out.