You clobbered your bootmgr by deleting the XP partition. Run this program
(it is the last entry on the webpage) which you have to burn to a CD and load from the CD reader (do not forget to change the boot sequence in the BIOS unless the CD reader is set as first already).
Once PW ("this program") is loaded, highlight your Win7 partition and make it "active - the control is under the Partition tab > Modify. Make sure there is no other active partition on the drive, else deactivate that other partition. And do not forget the APPLY which on the bottom left.
Now you can rebuild your bootmgr like this: Bootmgr is missing - Fix