Just some general things to try at first.
Go to http://housecall.trendmicro.com
and click the Scan Now link to run a free on-line virus scan.
You need to be running a firewall like free Sygate from http://download.com
- type, sygate, in the Search box, you must be on-line to register Sygate, that is if you're not using a firewalled Router on a Network or, have another third-party firewall like Sygate installed, to protect you and the Internet community from hackers, spammers and terrorist from using your computer for their own illicit needs while you're on-line?
Get, install, update and run free Ad-aware (and its HexDump plug-in) from http://www.lavasoftusa.com/software/adaware/
First in the main window look in the bottom right corner and click on Check for updates now and download the latest referencefiles.
Make sure the following settings are made and on -------ON=GREEN
From main window :Click Start then Activate in-depth scan (recommended)
Click Use Custom Scanning Options' then click Customize' and have these options selected: Under Drives and Folders put a check by Scan Within Archives and below that under Memory and Registry put a check by all the options there.
Now click on the Tweak button in that same window. Under Scanning engine select: Unload recognized processes during scanning and under Cleaning Engine select: Let windows remove files in use at next reboot
Click proceed to save your settings.
Now to scan just click the Next button.
When the scan is finished mark everything for removal and get rid of it.(Right-click the window and choose select all from the drop down menu and click Next)
Restart your computer.
Check your available resources by right-clicking My Computer; clicking Properties; Click the Performance tab. Resources available are displayed as percent there at top. Check it when you get done running the System Configuration Utility mentioned below.
Click the Start button; Run; type 'msconfig', without the quotation marks, in the Run box and click OK; Then click the Startup tab; Uncheck anything you don't need running in the background. For reference on what's not needed running in the background in the System Configuration Utility, view this website first and print out the list:
It's important that you print out the above mentioned list. The site provides a printer friendly link.
In the System Configuration Utility (SCU), you can uncheck programs you suspect one at a time and restart your computer. If something doesn't work right, you can always go back into the SCU and re-check it and restart your computer via the Start button. The changes are completely reversible by re-checking an item in SCU or by selecting Normal Startup under the General tab in the SCU and all the programs listed run when Windows starts as it was before you started.
Have you booted to Safe Mode and Defragged your computer lately? ScanDisk as well.
What anti-virus program are you using?