mb working and not working!!

Hello, I recently stepped into this problem with my custom built system.
First my config.
mobo: WinFast K7NCR18D-Pro
Processor: AMD Athlon XP 2100+
Memory: 3 Kingston 256MB PC2100 266MHz 32x64 DDR 184Pin
Videocard: maddog predator MX 440 8X GeForce4
HD: 4 maxtor 160 8MB
Power: Kingwing 350W

OS: Multyboot WIndows 2000pro and Mandrake Linux 9

The problem:

The system has been working perfectly for little more than a year, I only
had to replace a faulty PSU long time ago.
About 3 weeks ago when pushing the power button I didnt hear the bip that
usually is followed by the bios screen and the OS boot up. Holding the power
button for 5 second restarted the machine, bootup fine either on windows or
linux.
Few days later the same problem became more relevant, I had to restart about
4/5 time befor the bip came along and the bios screen.
To make it shorter now the behavior is even worse.
Powe button pushed, fans workin, no hd activity nothing on screen, traying
again for aout 20 30 times I get lucky and I see the cdrom light blinking
and the bios bips and the welcome screen, windows starts booting up, here I
have to scenarios, the first windows bootup screen the black with the white
progress bar, at soon as the progress reaches the end I get back screen and
only the fans are working, I have to restart again, if the progress bar can
reach the end the next windows screens appear and with the blue progress bar
reaching the end again everything goes balck, restart (well I have to
restart dozen of time to get to the windows bootup again) and if a get lucky
and widnows passes the firts 2 booting screens everything works fine until
the next reboot.

What I did to find the culprit:

Unplugged everything, only mobo and processor, no results
Unplugged only the HDs, again nothing
Unplugged video card, memory, cd rom and whatever is unpluggable in many
different order...nothing, still same problem.

I changed the battery and cleared the cmos, nothign again.

Every cables seems to be well plugged and just in case I disassabled the
entire system and rebuilt it again cleaning dust and ect.

No luck.

Any idea or just a stop to a computer store and buy a new mobo?

Thanks in advanced