Help! GTX770 problem in Vanquish 4

Not sure if this is the right forum section. I bought a Vanquish 4 a year ago during the sale. It has the EVGA gtx770 in it. Ever since I got it I have had problems with it crashing to a solid screen and having to be hard reset (I say solid color because it can be white or black or blue or brown - might be related to background color at time). I have been through a year of trying to fix it with DS (checking temps, memory, HDs, etc)and have just had to reinstall the OS (Windows 7) in the hope of fixing it but to no avail. Typically crashes within first hour from boot and then most of the time (though has crashed 3 time tonight) it is good for the rest of the day. Crashes on low intensity items like internet, e-mail but runs fine on high load games. Just wondering if anyone out there with a similar setup (Vanquish 4 with 770 card) has had the same trouble and been able to fix it. Crashes every day so getting tired of it especially as this is supposed to be a well tested system that they have built many of - any help appreciated.
Thank you.