If you think your computer may have a virus, you should do the following:

1. Disconnect your computer from the network. Many viruses, trojans and other malware transfer data off of infected systems. Until the malware has been removed, you should not be connected to a network. Otherwise, your data and that of your customers is at risk.
2. Back up your data immediately. If you can't, then call an IT professional. Have them image your system before they start working on removing the malware. 
3. Download tools to remove the malware. Great tools include Malwarebytes, Combofix, Spybot Search & Destroy and many others. Download them and run them in safe mode. If you can, go into the administrator profile on your system to run them. If you don't know how to do this, contact your IT person and have them help you. 
4. Verify that your system is cleaned up.
5. Make sure you don't have a rootkit; if the same malware keeps showing up even after you've cleaned it, then you might. If you do have a rootkit, then rebuilding your system is often the only way to remove it. Ask your IT person to rebuild your system at a fixed price. (Hint: Make sure they are doing this at a bench at their office and not sitting in your office. Otherwise, you will be paying for the time they are sitting there...which can be a long time.)
6. Once the system is clean, back up your data again. 
7. Install tools to help prevent malware from infecting your system in the future. Malwarebytes and Spybot S&D are great tools to have.
8. Start using a browser that is a little safer than Internet Explorer. Chrome and Firefox are great browsers and safer because they don't use ActiveX. Use those browsers for surfing and Internet Explorer only when you need ActiveX. 
9. Make sure you have great anti-virus and SPAM protection.
10. Make sure you are updating Windows every week. 
11. Make sure you also update Flash, Adobe Reader, QuickTime and Java every month. 

You may also want to consider having your system imaged every so often so you can have it restored to that point in the future if problems occur.

Finally, if you can afford to, reserve one computer for surfing and another system for work. You are much less likely to have viruses and other malware interfere with your valuable work data. Unfortunately, the Web is no longer a safe place, so be careful out there. 

If you have any questions, feel free to email me.