Mark Partition Active
Hiren's BootCD v8_1 may have a program that can fix the mbr.
Best option though is to CALL hp and tell them pressing F11 doesn't bring up the app, that you need to recover the machine.
I needed to restore the windows partition but pressing F11 didn't do anything. Luckily I could still boot into windows. With Vista I was able to go to Computer and right click, then Manage, Disk Management, and then I saw the hard drive with 2 partitions, click on the 2nd partition which was still there and then Mark as Active - then F11 worked for me and I was able to use HP recovery utility. This only works if you can still boot windows, but may be of use to others!