Cannot Access C: Drive with XP On it

Ok, i've been reading A LOT of forums and calling a lot of people, and asking the Geek Squad guys at my job (I work at BestBuy), and so far I have NOT been able to fix this problem..

Mobo: Asus M2N32-SLI DELUXE
Processor: AMD Athlon 64 FX-62
RAM: 4Gig
HD: 320 Gig Partitioned (C: Windows XP) (J: Windows 7)
GPU: NVidia 9800 GTX+

About 3 months ago I was running into some security issues with 7. I was unable to transfer some files between my C: drive with XP on it. I was able to resolve this issue by going under the properties of the drive, security tab, then add permission.
No other issues came up untill about a month ago. It completely denied me access to my C drive. Not only in Vista, but also when i reboot in XP I cannot access it.

Some fixes:
Used CMD prompt Net User Administrator /active:yes
Gave complete permissions to Administrator and my other user (Scott)
Gave complete permissions to Guest
Have turned on ALL file sharing options

Nothing is working.

I can completely modify, access, adjust and delete anything from Vista to the C: drive.
Once I reboot in XP i cannot do anything. I can only run programs. Every time i try to access the C drive i get the "Access Denied" error.

I want to continue to use 7 But im getting VERY frustrated with it locking me out of everything. Can someone please help me?

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