Windows 7: Computer Won't Sleep

So I reinstalled Windows again on my machine about 3 days ago, and in the process of reinstalling my old programs and settings, my computer has stopped sleeping automatically. Before I had installed very many programs, my computer was set to sleep after 1 hour and did that every time. Now, the setting is still the same, but I'm assuming some device or program is preventing it from sleeping. The monitor turns off at the right time, and the sleep button on my keyboard puts the computer to sleep, but it won't do so automatically. Is there any utility or method that can help me troubleshoot what is preventing my computer from sleeping? Thanks!

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Update your Display driver. This is almost always the culprit. You may even need to try the next oldest driver, or a Vista driver.

Check optional Windows Updates for newer drivers, then the Support Downloads webpage for your computer or Display adpater model.

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In addition to your display driver (as suggested by gregrocker), check your mouse, USB hubs and NIC settings. Using control panel make sure that the "allowed to awake" options are checked/unchecked.

Okay cool thanks

Thanks for the replies! I'll give those a try.

I had this same problem with my Laptop.
The fix for my Laptop was in Advanced power settings.
Open sleep settings.
There was two sleep types.
Hybrid.
Hibernate.
Apparently with my laptop you cannot have both those sleep patterns going at same time.
So i just set Hybrid to OFF.
And i just use Hibernate setting for laptop sleep modes.
Solved my no sleep problem.
Hope that helps.