Ok on my dell inspiron 1521 i have vista home premiumand i boot up and it gets to the loading bar and right before where you can choose you username it goes into a startup repair but it restarts and keeps doing this in a loop. Well i have booted up with the vista home disk and repaired it repairs the boot manager every time i boot or boot from the disk.
More aboutdell inspiron 1521 repair problem help
Sounds like a MBR / boot partition foul up. . the easist thing is to do a ocmplete reinstall. . . doing another repair will mostlikely screw tings up worse.
But you might want to try a live spin just in case.
the simpliest thing is to do a "format C:" and reinstall SO. if you have do a complete backup of all files, you'll don't have any trouble in formatting