Mobo with blinking pw LED. Doesn't start

[osidovich]

GA-H55M-USB3 rev. 1.0 motherboard.

Yesterday OS (Windows 7) starts to freeze. Symptom: screen garbled with stripes.

Powered off and on.

Sometimes POST was successful, OS boots, I was able to login into Windows and to use some programs but after some minutes, screen was garbled and system freezed.
Powered off and on, again, system was stuck at POST stage.

CPU fan and other fans are running, LED inside motherboard on but power LED repeatly blinking.

After some cycles of power off/on, I've heard 1 beep of POST and system started but, after some minutes of use, problem reappeared.

Today, system doesn't boot.

CPU fan and other fans are running LED inside motherboard on but power LED repeatly blinking.
If I remove graphics card, system blinking briefly, shut down, restart and, after some blinking, has 1 long beep and 2 short beeps and I see HDD LED activity. I'm unable to check if something boots.

If I reinsert graphics card (Radeon HD 5670), system remains at:
CPU fan and other fans are running LED inside motherboard on but power LED repeatly blinking.
After some minutes without user intervention, it shut down.

I've done Windows Memory Diagnostic, before stall, without issues.
Removed quite all RAM DIMMs.
Detached SATA HDDs.
Shorted CLR_CMOS jumper
Removed and inserted CMOS battery

Without benefit.

I don't have a spare motherboard, PSU or graphics card to check.

Personally I think that is a graphics card  issue but before buying another one and, in order to resolve it fast, I need some advice.

What do you think?

Thanks.

[autotech]

Does  you CPU have onboard graphics if so that rules out graphics. which leaves cpu.

[osidovich]

Does  you CPU have onboard graphics if so that rules out graphics. which leaves cpu.

Motherboard doesn't have onboard graphics.

My CPU is i5 760 socket 1156

[shadowsports]

If the striping you are seeing is uniform colored blocks.... I'd also memtest my memory.   

[osidovich]

If the striping you are seeing is uniform colored blocks.... I'd also memtest my memory.   

Now I'm unable to boot or pass POST or see output on monitor, so I can't test memory.
Last memtest, before the full "blackout", was OK with no errors.
Stripes was verticale, grey and white.
I've also experienced a full screen white and a Windows BSOD, as stall conditions.
Memory dump analyzed showed an error in dll of video card drivers.