The hard disk and the OKS aren't relevant at all. The BIOS will boot quite a long way without any hard disk (or cd or USB-drive or diskette) connected.
If you don't see any sign of live from the BIOS, it's either the PSU (power supply) or the motherboard (including the CPU) or the video card (if you have a separate one) or the monitor cable or the monitor that has gone south. It's up to you or the repair shop to find out which of the five.
I've ran into a big problem, when I started up my computer one day the screen will not display any sign of activity on it anymore, Now everything is installed, all of the wires attached, I bought a new hard drive and installed into my old desktop (Windows XP Home Edition 2002) Im pretty sure of the year, anyways that's all I've got to say for now If you need anymore information about the desktop, let me know and Ill give you all of the specifications