I don't know how to permanently fix the PC clock but I do know of a utility that you can download off the NIST website to correct your computer clock time as needed. It is located at http://www.boulder.nist.gov/timefreq/service/its.htm
The NIST runs an atomic clock in Fort Collins, CO, so that is about as accurate as you are going to get. NIST are the same folks who run WWV, the time station.
The utility can be used to update when ever you request it to or it can be set to update automatically at intervals.
Click your right mouse button on clock on right side of Windows taskbar then click with your left mouse button Adjust Date/Time in the pop up submenu;
Now click Internet Time tab with your left mouse button then locate time.nist.gov in the drop down menu and then click Update Now with the left mouse button. Then click OK. Your taskbar clock should now be synchronized with the U.S government's atomic clock time servers on the Internet.