PC monitor keeps going black but the tower still runs

[sharpo1]

hello there, my desktop PC keeps randomly having the monitor go black with a message coming up saying no signal however this is not all. if i am watching a video it will loop the sound also, so its just turns into an elongated humming noise. does anyone know what to do? i have taken it to a technician he said he took it apart and rebuilt it and left it on for around 2-3 days and this didn't happen. over the course of 10 days he tested what he could and still did'nt know. i got the pc back around 3-4 days ago and it's only just started happening again. i have 7 fans and a big cpu heatsink so im not sure its temperature.

the computer remains on and humming normally throughout all of this. i have tried different hdmi cables also and no difference.

what info would you guys need?

[Avtrician]

Perhaps the video card needs replacing..

[rgbrock1]

Have you tried connecting a different monitor to see if the same thing happens? If it does then that means it's probably the video card. If it doesn't happen that means it's probably the monitor.

[sharpo1]

hey there. i built the computer myself.

i am using an MSI X99 sli plus motherboard

16gb ddr4 crucial ballistix ram 4 sticks at 4gb each

intel core i7 5820k 3.30 ghz cpu

64 bit windows 8.1

EVGA geforce gtx 970 graphics card

EVGA super nova 850w psu

be quiet! shadow rock2 heatsink

one 140mm mill fan at the top facia back sitting intaking

one 120mm fan at the bottom facia front sitting intaking

two 120mm fans at the front facia bottom sitting intaking

one 120mm fan at the back facia top sitting exhuasting

plus the heatsink fan and the 2 gpu fans.

as far as im aware all my drivers are up to date.

UPDATE
__________

it's started making black/white lines flash horizontally across the bottom of the monitor just before it goes black now. literally for a split second. however it sometimes recovers after it goes black and then proceeds on normally (as if nothing is wrong) for however long.

[Saab Dastard]

Has it behaved like this since you first built it, or is this a recent development?

Have you overclocked the system?

Have you run Memtest on all the RAM modules?

Have you ensured that all the components are correctly seated? I'm assuming you applied paste when mounting the heatsink on the CPU!

Have you tried attaching a different monitor, as rgbrock1 suggested? I suggest that you change the VGA cable at the same time.

Can you obtain a different graphics card?

Have you checked the system event logs?

Have you got temperature monitoring software (e.g. SIW - no longer free, sadly) to see what temps your GPU, CPU HDDs are reaching?

SD