system does’ntt boot up or recognise HDD

Soemtime, when I boot up all i get is a blank screen, no post on beeps of any description.

I changed HDD cables and positions, but the error repetas itself. Only after shutting the system down (all power off) I cna get the machine to boot up troble free.
Can anyone help solve the problem.

Here are some System info

Processor: AMD Athalon 1GB
HDD : 1 IBM 20GB
HDD: 1 IBM 10GB
RAM (matched): 512KB
OS: Win XP Home
Motherboard: Gigabyte