Sleep issues are often caused by the Display driver. Update yours, or try another version. Older drivers are queued at Device Manager>Display>Driver>Update>Browse>Let me pick.
If this only occurred recently, try a System Restore
to a point before it happened.
Have you used any tweaking suites or optimizers on Windows 7? What AV and firewall are you using? We recommend absolutely no tweaking beyond normal System settings, Microsoft Security Essentials
with the Windows 7 firewall for best performance.