Dell C521 wont boot (again)

It gets to the windows loading screen, starts the flag animation, but restarts the computer.
I press F8 at startup, but i dont get the menu that would usually pop up. It just tries to boot. I can hook the HDD up to my laptop and view files just fine. I just need this PC because it has better specs and i need to do a stream :/

SPECS:
Windows 7 Home Premium x64

AMD Athlon X64 Dual Core Processor 2.0GHz 3800+

8B Unbuffered DDR2 RAM

PCI SLOT 1 Empty; 2 Empty; 3 Network Card

Hitachi HDS725050KL 500GB HDD

Sony CRX310S CD-RW/DVD ROM

Integrated Video Card Memory Size: 128MB

Dell Dimension C521 Small Form Factor Desktop w/ BIOS version 1.0.3 (10/02/06)

(EDIT: Startup repair wont fix it, i tried.)
(ANOTHER EDIT: How can i change boot mode to AHCI?)

Boot into System Recovery Options on the Win7 install media or System Repair Disk to confirm 100mb System Reserved partition (preferred if you have it) or C is Partition Marked Active then run Startup Repair - Run up to 3 Separate Times . This should ask you if it can automate System Restore, but if not and it fails run System Restore from the Options List.

If this fails work through the steps from the top for Troubleshooting Windows 7 Failure to Start which compiles everything that can possibly be done.

But if this is the original factory preinstalled Win7, it's the worst possible install one can have which no tech enthusiast would run, so I would use this oportunity to do a Clean Reinstall - Factory OEM Windows 7.
Everything needed is in the blue link to get and keep a perfect install.

As it says in the Special Note to Dell Owners at end, boot into F12 to run Dell Diagnostics to test the hardware, then if it works I would only keep the Dell OEM partition since Recovery will not run after a Clean Reinstall anyway. So delete all but the Dell OEM partition during Steps 7 and 8 of Clean Install Windows 7 which is the illustrated guide to the actual install.

Before reinstall reset the BIOS to defaults after entering BIOS setup using the key given (F2 is likely) on first boot screen. There you will also find the SATA controller setting to set to AHCI.

If you insist on trying to repair this install work through the steps for Troubleshooting Windows 7 Failure to Start.

Just doing a clean install.