Hello all.
If you have this problem: i.imgur.com/VdloVqD.jpg , Folow these few quick steps to help you play again:

1) Back-up your CS:S CFG folder and if you have a custom GUI back-up the Resource map.
2) Uninstall CS:S from Steam.
3) Log out and back in on Steam
4) Download CS:S
5) Put your config back and voilá
6) Play

;-)

Good to see the good advice from hrizn, however, just restarting steam will fix this without naffing about