Im copying one of my posts in here, as I think it is good advice to avoid Electro Stactic Discharges.

If you work on a PC, and that PC has a three pin plug, (where one is earth), and a power switch to cut power to the system - you should only cut the power via the switch, and leave the plug in as it provides earth. Then as you work on the system, ensure that you make regular physical contact with the (unpainted) metal frame, either by grabbing it for a few seconds, or using, as suggested, an ESD wristband.

For some more info

http://www.webopedia.com/DidYouKnow...2002/static.asp

Also try and ensure someone else is around incase you have a problem.

Be safe...