Hi,
What exactly is the:
Motherboard: name and model?
CPU: name and model?
Memory: size, how many sticks and name and model?
Graphics: name and model?
Perhaps You have a problem with the memory sticks?
Are You sure that everything is properly mounted?
It could be problems with the memory, so that is where I suggest to start, well but first:
0. Unplug the power from the wall outlet.
1. Be careful of the ESD (Electrostatic Discharge) and try to use an ESD wrist strap attached to a non painted metal part of the chassis.
https://en.wikipedia.org/wiki/Electrostatic_discharge
https://chioszrobots.files.wordpress.com/2013/09/antistatic-wrist-chiosz-robots-3.jpg
2. Check that all memory sticks are properly seated in their slots.
3. Check also all connectors, graphics card and its power connectors, so everything is properly mounted.
4. Test Your memory's
Run memstest86+ Download and install Memtest86+ it's a free s/w http://www.memtest.org/
Create a bootable CD/DVD or USB-stick, it is a very small program, it will easily fit on a CD.
Then boot the computer from this, memtest will automatically start, and don't worry - it will not in any way compromise nor touch anything on the hard drives.
You must run memtes86+ until at least pass 8,9,10 and 11 (it uses different test pattern then) and for 8GB of memory with an Intel 2600K it will take the whole night, approx 4-5 hours, if 16GB memory - twice as long.
If an error occur, You can just shut it down. Then You know that it is a serious problem with your memory's.
Take out all memory stick but one and run the test again - it will be much faster.
If no problem, replace the memory stick and run memtest86+ again so that you now which memory stick is faulty.
In case of a RMA, all memory sticks in a memory-kit must be returned.
Best regards from Sweden