How to repair windows registry?

I shan't knock you for buying dell you seem to have learnt your lesson, Do you have a windows installation cd? if so pop it in, check in your bios that the cd drive if the first boot device. Boot from the cd and it has a repair option to repair your installation of windows. Some laptop manufacturers also include a repair feature built in so to speak. You may see a promot during the early stages of the boot process to press a key to repair you could try that.