Windows restarts in case of any stop (ie. Windows stops responding, or a [corrupt] file causes a critical system error). Some file is likely corrupt in the files required to boot, causing it to restart.
To find this file, hold F8 down just before Windows starts booting and continue holding it until advanced boot options show. Select Safe Mode with command prompt. Watch and see how far it gets before it restarts, if it restarts. Let us know the results. Also try replacing the ntdetect and NT Loader files,
as shown here.
First thing I would do is to disable all performance functions in the BIOS, especially those related to RAM. Also, specifically try having the memory hole enabled as well as disabled. Windows locks up or reboots if that specific memory address range cannot be overwritten. Some systems will only work with it enabled, others only with it disabled.
The next thing to try would be to press and hold F8 as Windows starts to load to get the boot options. Go to Last Known Good Configuration.
If those don't work, try to use System Restore. To do this, you'll have to go to the boot options again by holding F8 as Windows begins to boot. This time, select Safe Mode with command prompt. Run %windir%\system32\restore\rstrui.exe with %windir% being your Windows directory.