PC not booting\freezing - MB\RAM\PSU faulty? Multiple short beeps most of the time.

Hi folks,
I'm posting this question, because I am at my wits end as to the cause of my pc's problems.
Sorry but this will be a long post and it will look a bit incomprehensible, but english is not my native language and I'm pretty angry:<

TL;DR PC freezes and\or won't boot 80% of the time, long series (~30) of short beeps, tried different combos of RAM and GPU, doesn't help in most cases.

So here goes, first the specs:
CPU: Intel 3570k (no oc)
RAM: 4 x 4GB Corsair XMS3 CMX8GX3M2A2000C9, 2 x rev. 5.12, 2 x rev. 4.13 (no oc), default 1,5V
MB: Gigabyte Z77-DS3H
GPU: ASUS 670GTX DirectCU II (no oc)
PSU: bequiet Power Zone 630W
Main SSD: Crucial M550 mSATA
Other hdd's: 4 x WD Green, 1 x Crucial m4 SSD
OS: Windows 7 Home Premium x64


It all began a few weeks ago my PC crashed. After some subsequent rebooting and testing I found out, that this was due to the PSU having a defective fan, it overheated and crashed the rest. Unfortunately my MB (had a ASUS Maximus V Gene) was broken now and detected only half of the ram modules. This was tested with memtest. I've sent the PSU and MB to repairs.

Yesterday I've recieved a new PSU replacement and also a new mainboard (the gigabyte listed above), since my "main" mainboard was sent for repairs and I've needed a temporary solution.

Booting the system for the first time went fine, it could see all the ram modules (16GB in total) and I've proceeded to reinstall the OS etc.

After a few hours of confuguration chores I've decided to play some Divinity Original Sin. After about 30 minutes my PC froze. There was still the last image on the monitor and fans were working, but the system would not react. After a reboot there was a long series of short beeps (about 30 beeps) and the pc rebooted again, with the beeps. I've shut it down and disconnected the psu, conencted it again but the problem persisted.

The first thing I did, was to remove the memory modules and run some tests with memtest. The tests were run in SMP mode in slot 2:

- rebooting with no mem modules insterted resulted in the long series of short beeps, so no short series of 3 beeps indicating a memory problem

- memory modules - lets call them "5.12A" & "5.12B" didn't pass the test: http://imgur.com/a/nZe2B

- memory modules "4.13A" & "4.13B" passed them (few runs). I thought I have found the issue here, but when I've inserted both in Slot 1 & 2, memtest stopped at test #7: http://imgur.com/a/QCtme

I took out a memory module from slot 1, left the one in slot 2, which woked fine before. After rebooting the PC the same problem as before occured, that is a long series of short beeps. Now I have begun to have doubts about the new PSU replacement that I have recieved.

I've shut it down and reconnected the power cable, powered up - beep series.

Powered down again, reconneded all power cables connecting the PSU to the MB, GPU and drives. Powered up - boots fine!

So now I want to check on the voltages of the PSU, I have no hardware device to do so, so I've used the MB utility software and HWMonitor: http://imgur.com/8bxJtdK

Everyting seemed fine, but just to be sure I ran PRIME95 for about 15 minutes, the voltage didn't change more than 2% on all voltage busses.

Now I didn't really know how to proceed. I did a warm reboot and the pc booted fine.

I've took out one of the 4.13 modules, the pc powered up, went off and powered up again, the now well known series of beeps followed. Turning the PSU on and off didn't help.

I've disconneted the GPU for the PSU. Powered on, a message about the need to connect bot (2 x 6pin) cables showed, powered off, connected cables, powered on, the OS boots! But now I only have 4GB of the 16GB I intend to use.

Powered off again and for tests I have swapped the 4.13 modules (4.13A for 4.13B). Powered up, again the short beeps. By now I thought that maybe the GPU or the 5v bus (for the SATA drives) is being overloaded or defective.

So I've disconnected the GPU completely, booted with the internal GPU and both 4.13 RAM modules. The OS booted up fine, subsequent soft reboots went fine too. Powered off, inserted the rest of the RAM modules, powered up - series of beeps. Removed the 5.12 modules, powered up - beeps again. No I knew it wasn't the GPU. I've connected it again.

After the previous I've disconnected the SATA power cable from the PSU. The OS booted fine (with both "4.13" mem modules). My first thought was, that somehow the SATA power bus must overloaded. But first I thought I'll do some stress testing on the rest of the components. Evrything went fine for about 30 minutes of running furmark and prime95 at the same time, screenshot from about 5 minutes in: http://imgur.com/PPKL0Oq

When the test finished I moved the mouse cursor and WAAAGH! the PC froze again. Rebooting the PC resulted in something new - I've got 2 series of 3 long beeps. AFAIK the BIOS signalises with it, that there is a problem with the keyboard interface, however after some googling around I've found this post from THW: http://www.tomshardware.co.uk/forum/306576-30-long-beep-trouble-code

Powering off and rebooting again allowed me to boot the OS and write this post. Now I have no clue what to do next.

Some other tests and observations:

- Upgraded BIOS to the newest version (F9)

- Intel CPU Diagnostic Test, ran a few times, everything is green

- Sometimes the PC freezes shortly after the OS boots, with no load at all. After a reboot I get the beep series most of the time.

- AFAIK there is no official documentation from Gigabyte on the long series of beeps, it's suggested on the internets that this could be either a problem with the power supply or ram modules.

Is it possible that, after the original PSU failure all or 3 of the 4 RAM modules are faulty? Should I RMA them?
I'm going to purchase a voltage meter soon to do some tests on the (brand new!) psu.

Now I am writing this post on a machine that could freeze any time. Any suggestions and helpful tips are most welcome! Sorry for the long story but I didn't want to miss out on anything.