The cheapest upgrade

My system:
MB GA-M57SLI-S4 (rev. 1.0)
2x1 GB Apacer PC6400 DDR2
AMD Athlon X2 Dual Core 3800+
2x250GB Samung 7200rpm SATA2 8MB
Gigabyte 256 MB DDR3 PCIE16 7600GT
power - fspgroup 400W ATX-400PNF
Midi tower case

(you can skip to the last part, if you are not interested in reasons, why I ask for the advice)

Bought the system in early 2007. After 1.5 years it went dead, but was fixed under guarantee (something burned out on MB).

I have dual OS system - Windows XP for games and Ubuntu 10 for work. My system works in always on mode. Yesterday, when I woke up, I found system halted under Ubuntu. I pressed Reset on the case, system switched off, then back on and nothing happened. Meaning - I heard the sound of HDD spin-up, all coolers start rolling, but monitor shows "no signal". And no BIOS beeps, cause it must beep once, if all is ok, or more, if something is wrong.

Using my friends computer, which has almost the same hardware (we bought our computers together), I tested out, that RAM, HDD, CPU, VIDEO worked fine. Then I plugged his hardware in my MB and it still didn't work. So, I figured, that MB has died on me.

I searched all local retailers, but nobody sells GA-M57SLI-S4 anymore.

I tried to make a research of my own, but got desperately lost in armadas of available MBs and my lack of knowledge of today's hardware compatibilities.

Mortgage takes all my financial resources, so even 400$ for me is too much. 100$ would be accessible amount of money I can spend on fixing this problem.


Last part.

Based on my system, what would be the cheapest modern (available at most of the retailers) upgrade for MB, so that I would need to change the least number of components?