A while back I upgraded my computer and only recently discovered that I've got problems with encoding in x264 format and it's variants in ALL methods of video conversion. Attempting to convert ANY format to a h264-encoded format results in whatever program I'm using for conversion crashing or halting conversion after just a few seconds, be it Any Video Converter, Handbrake, or VLC Media Player's convert/save feature. However conversion is slightly possible, as if a video is converted quickly (e.g. by lowering the output's resolution) then the video can play normally however it has very heavy artefacts. While I can use Sony Vegas to simply import a video and then render it in a format that uses a h264 codec without it crashing, the end result still has heavy artefacts.
I know the problem isn't to do with my files or any kind of media player as I have I have h264-encoded videos that I've downloaded and saved before I upgraded and they play perfectly fine without any artefacting or problems.
I'm using both Windows 7 and Windows 10, both on separate SSDs, and the exact same problem persists across both OS's. I've also tried fully updating both of them to no avail (however it did fix a small AVI problem Win7 had with Vegas)
The problem is unlikely to do with any additional codec packs I may have stupidly installed in the past as the problem persisted even when I did a clean install of Windows 7 and attempted conversion the problem was exactly the same.
I've also attached an example of what happens when I "successfully" convert a video into h264. It's just a snippet of old Dark Souls 2 footage I was using for sound effects a long time ago. example.zip

Asus Maximus VIII Hero Motherboard
Corsair 16gb DDR4 3000Mhz RAM
Intel i7-6700k CPU (has not yet been OC'd)
MSI Gtx 980 ti
Corsair RM850i PSU
Windows 7 + Windows 10

And for the record, I'm looking for a solution, not an alternative.