I erased the partition with my on it?

I was in the process of erasing ubuntu and installing xp when in the xp installation process I accidently erased the partition with linux on it. Now when I turn it on it says os cannot be found. I don't have the recovery disk for my laptop (lenovo n100 3000). And Linux will act like it's gong to load then bring up a log in name. And I didn't even set up ubuntu it just does tHat. I have no idea what to do. Can anyone please help?