All source games crashing/black screen

[Miss Napalm]

I've just spent a fair bit on a new system and it's running things great (Avg 120fps on Tomb Raider Benchmark). My problem is whenever I load a Source game I keep getting errors.

For Half Life 2 and its episodes I get a black screen but can hear the sound my mouse makes when it hovers over menu items and when I click them it makes a white box appear at the top right of my screen. For Portal 2 it goes as far as the loading screen then just crashes.

Specs
Intel i7 4770k
8gb G-Skill Ram (from old system, passed tests)
2 Matrix Platinum 7970s in CrossfireX mode running latest non-beta drivers (errors occur with crossfire disabled as well)
Seagate Barracuda 2TB HDD
128gb Samsung 840 Pro (OS Drive)

Any help would be great. Will provide any more details if needed

[Kiya]

Have you added a new monitor as well? If you transferred the game files over to your new system with a new monitor then the resolution for the games may be set for your old system.

If you think that might be the problem, in the steam client, right click on one of the games in your library list, select properties from the dropdown list, then in the General tab select 'Launch Options'. In the box that comes up type -w (your desktop resolution width) -h (desktop resolution height) without the brackets.

Then try launching the game