Start> Run >> Msconfig

Go to the Startup tab, and disable everything.
Go To the Services tab, check the box that says "Hide all microsoft services" then click disable all.

**NOTE,: Be sure to remember what is checked, and what isn't!!**

Reboot, then try.

This will isolate the possibility that something else is running in the background eating up virtual memory.

If it works, start enabling some things. Start with the first half, then test. If it works, do half of what is left, and so-on and so-forth. Narrowing down what is causing the problem.

If it STILL doesn't work the first time round, then something in your Windows system, or something in your game is the problem.