I'm having a nightmare with this system I put together for my Mum.
I'm re-using the Asus M4A785TD-EVO motherboard http://www.asus.com/Motherboards/M4A785TDV_EVO/ and Athlon II X3 425 CPU that my Dad was using as his own system until a week or two ago, when I built him a new Intel PC. I'm also using the 2*2GB Corsair Ballistix Sport 1333Mhz DDR3 that he used to use in that system until I bought him a 8GB set a year or so ago. I replaced the old noisy PSU with a new Corsair CX430 and installed a new Transcend 128GB SSD (no HDD). It's running Win8.1 Pro Update 2 x64.
When I was building and testing it at my house, I didn't encounter any problems but within hours of hooking it up at my Mum's house, it had crashed with the screen covered in a mishmash of colours. I'm using the onboard IGP, which can be set to Sideport (to use the onboard 128MB sideport RAM), UMA (to use the system RAM) or Sideport+UMA, which is what I had it on initially, so that it could use the faster Sideport RAM and the system RAM if it needed more (the Sideport RAM runs at 1333Mhz, same as the system RAM, although it can be set to lower speeds in the BIOS). Then I changed it to Sideport only and a few days later my Mum reported that it had locked up again, so I changed it to UMA only. It turned out that it hadn't actually locked up, her mouse had just stopped working and unplugging it from the rear of the PC and plugging it into the front USB sockets got it working again but she reported she still had problems with it, so my Dad swapped his mouse with hers and didn't have any problems and she didn't have any with his, so they've swapped back now and it seems to be OK (still plugged into the front socket at the moment).
Anyway, it still locked up whilst on UMA, with the same colourful mess on screen. Once I saw it lock up with only a few tell-tale lines of colour, as we were doing Windows Updates and thought it was stuck on 0% until we realised it had locked up but most of the time it covers the entire screen. I'm losing track but I think I've set it back to Sideport only again now but I'm not sure if it's already crashed whilst on that or not, so I'll have to see what happens over the next few days. Occasionally, the monitor goes blank and then comes back on, which could be a problem with the monitor or the PC but it didn't do it with her very old P3 system she was using with Thinstation up till now. My Dad was using an ATI HD4650 512MB PCI-E GPU, rather than the onboard IGP, as he needed it for X-Plane but my Mum doesn't play games so I was hoping the IGP would be sufficient for her. I'm running the most recent ATI legacy driver for the onboard HD4200, which is v13.1.
To top it off, the onboard audio has stopped working now! When I was testing it whilst building, despite having an HD Audio lead to the front panel I couldn't get anything out of the front socket unless I set it to AC'97 in the BIOS but it was working at my Mum's using the rear socket until the other day but now neither the front nor rear sockets are working. It's a VIA VT1708S, which does have Win 8 x64 drivers available, albeit quite old, one from 25-07-2012 and another dated 7-11-2012, which is the one I installed initially. My Mum's speakers are pretty rubbish but I plugged them into my phone and they worked, so it's definitely the PC. I've tried changing the drivers between the two and sometimes it seems to initialise with a thump (well, as much of a thump as flat speakers can make) and the right-channel will start working for a bit but nothing from the left one. I've disconnected the front panel header, just in case it might help but I did buzz it out when I was building just to make sure everything was connected and there weren't any shorts, so I don't know why it didn't work when set to HD rather than AC'97.
So I guess I'll have to buy a cheap USB soundcard for about £8 (it seems rather hard to find cheap internal cards and perhaps an external USB one will be a better option anyway) and put the HD4650 back in. I'm a bit worried about how many things seems to be going wrong though and don't want to waste money or risk anything else getting damaged if there's a fundamental problem with the hardware that's causing all these problems. Temperatures are fine as I'm using a mini Ninja tower, which keeps it between 30-40c under normal use, so I'm at a bit of a loss and would welcome suggestions.