yes reformatting will give you stability but maybe he dosent want to lose his stuff. Boot off of your Xp cd and repair the instalation like Blueman said and if that dosent work then make a fresh copy overwriting the old one and transfer all of your old documents and settings.(copy paste the old documents and settings folder and paste it over the old one) Defragmenting your HD wont be a bad idea if you make a fresh copy BTW.