I tried to install Ubuntu on a pc for a friend that sometimes freezes up in windows XP. (My thinking was that if it freezes up in Ubuntu then it is a hardware problem.) Just nearly finished installing alongside XP and it froze up and had to push the button. I was unable to login to the Ubuntu installation, it did not show a proper login screen and was unresponsive. So then using UBCD4Windows i deleted the main big Ubuntu partition. One problem is that XP did not show up at all as a boot option after that failed Ubuntu installation attempt. If i could get into XP again perhaps i could delete the Ubuntu partitions? Also have a big XP problem because i replaced a dead Motherboard and made rescue DVDs but they wont work unless Motherboard is tattooed.
Deleting the Ubuntu partition will solve nothing by itself, it will only make things worse.
Use a Windows XP CD to boot. If you don't have yours, any Windows XP installation CD should do the trick.
Then, when asked, press R to enter the recovery console.
Issue this commands:
And that's it, Windows should boot again. Now, you can delete the Ubuntu partition and try again if you want to.