Tearing my hair out

Dear forum members, I am very much hoping that someone can shed some light on my problem. I'll start from the beginning!

offered to fix a friends PC as it was running real slow, eventually came to the conclusion that reformatting the HDD was the best option.
All fine, up and running again.

Went to reboot the machine and got 2 short beeps followed by a pause and then another beep.

Bought a 2nd hand identical mobo and some brand new ram

Same problem

Bought another 2nd hand mobo & a brand new PSU

Same problem

Bought a 3rd second hand mobo

Same problem!

I am really confused, even with no hardware connected I get the same 3 beeps on all of the mobo's. Regardless of whether I use the original or new PSU, regardless of whether I use the new or original RAM, regardless of whether I use a P4 1.9ghz processor or a 2.4ghz processor (both which came from the same make & model of mobo)

Anyone got any ideas?

MOBO = Gigabyte GA-8SIML REV 1.0
CPU = P4 (1.9 or 2.4ghz)
RAM = 256mb (original) or 2 x 512mb (brand new)

When you power it up, the screen flashes 'packard bell' then goes blank and you then get the beeps as mentioned above.

The fault is identical across 3 motherboards, the original and the two replacements which I bought 2nd hand from two independant sources, both of whom are reputable.

Thanks in advance
Matt