Make sure that the command /usepmtimer is in your boot.ini file.
Using your mouse, right-click on My Computer go to Properties, click on the Advance tab, then under Startup and Recovery click on Settings, then click on EDIT....make sure your boot.ini has the /usepmtimer in there (located in the last line), if NOT then just copy and paste /usepmtimer in there.
By the way, if the above is not in the boot.ini file I would be really suspect. That entry should be made when the AMD dual-core optimizer is installed. If it is missing, then something has removed it.
Did you happen to do a restore? If so, then you probably need to re-install the AMD patch. If not, then you might want to start thinking about the software you run on your computer. If something is messing with the boot.ini file, you really want to get rid if it.