Running in admin.
Machine's custom built, kinda crappy now, was good at the time. It ran it literally the night before the patch without any issue whatsoever.
I'll try a full reinstall.
Thanks for the suggestions guys, much appreciated. I'll let you know what happens after a full reinstall.
So, alright. I've done extensive research on this problem. What happens is I start steam, go to launch TF2. It gives me the "Launching TF2" screen, and then it disappears. Nothing starts. HL2.exe doesn't even start.
Now, here's what I've done (according to my research):
Reinstalled video card...