Hp dv 5 not booting

Hello,
pls i hv a dv5 hp laptop, about a yr old.
i was workjn wit it at nite on my bed b4 i dose off, i woke up later in d midnite 2 shot it down but it refused . so i had to press and hold power boton inorder to shot it down.

d next morning when i try to power on the p.c it will only show *HP* then it will go blank.
at first, i touht it is a software problem so i insert a bootable cd but it did the same thing without showing the boot from cd opton. since then, i hv tried other things like replacing the ram , hard disk and even the processor but the problem continued
i dont no wat else to do.

sometimes after setting boot option, it will seem to reconise the hdd and cdrom but still the problem continued.it would go black after showing the hp logo.
to the best of my knowledge the display unit is ok.

pls i need help i still love my pc