Why won't my iPhone 4 restore?

I've jailbroken my iPhone 4 and I want to restore it so it's no longer jailbroken. Whenever I try to restore it, it fails and then iTunes doesn't recognize it. It does this everytime I try and I've entered DFU mode and it still don't work!

You tried using tiny umbrella?
if not try it! Might work!

The help support page apple got on this problem is not helping me out. My iPhone is in "Connect to iTunes" mode and when I restore it, it gets passed all the steps then it says "This iPhone can't be restored for an unknown reason". I'm going to try to restore on my other PC so I'm hopping that works.

I also just restored my PC to factory settings also.

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