i just build a new pc and i couldnt wait to start it on (i havent got yet the new HDD) so i took my dads hdd with the OS and i connected it and start the computer.
after doing that i got some errors and some blue screens, so i connected the old hdd to the old computer and after doing that the computer start on and nothing appear on the monitor and than it beeps like for 5 sec, so i tried to boot-up without the hard drive XD and it gave me the same problem (beeps for 5 sec and the reboot).
You're in the wrong thread first of all. You can't just remove a HDD from one computer, and put it in another without reinstalling the OS. Your issue with 5 beeps could be memory, or processor. Just RTFM, to find the error codes.