Windows 7 dual boot problem?

I have a computer that I run with windows 7 and it works fine, until now. I attempted to make a dual boot with windows xp so that I could play an old computer game and now the computer won't work at all. Now at startup I just get a black screen with a blinking cursor, and before that I had all kinds of problems. This game is definitely not worth it. Any way I attempted to install xp on a partition I created on my main hard drive and I read that windows 7 won't boot up because xp overrides the MBR or something like that. So is there a way to erase the partition with xp on it so that I can go back to just having windows 7 again? Remember I can't get into the OS as of now so it will have to be done through the bios or some type of bootable disc. Please help