well, when given information how to fix something on one computer, be wary of trying it on a different computer as things like this can happen. with HP computers (all that i've seen) when booting you can open the boot menu and select the recovery partition and recover that ay. not making it the active partition.
as far as re installing,
are you using a oem cd or a burned copy?
does the cd boot when you start the computer or does it just pop up sayin cant find ntldr?
if the cd boots and goes through the install process til where you would select the partition, is there just not a hdd (hard drive) there at all or does it show a hdd without partitions?