I have an hp pavilion 503n. this computer has never given me any problems whatsoever. i sold this computer recently to a friend, and i had it all clean and ready to go, and i just had to put in a dvd-rw drive. i unplugged the computer, put the drive in, and when i tried to boot back up, the system would not boot. all fans started, power light came on, and both cd and dvd drive read lights came on as usual, but no video signal, and the hard drive LED never lit up. what should i do?