Do you really need to stop thinking about them completely? I mean if you try to block them all out it's going to be harder on you. Try thinking less rather than stop altogether:)
No way to stop it. Keep yourself busy, and as time goes by you'll find yourself thinking about it less and less. Hourly thoughts will turn to daily thought, daily to weekly, weekly to monthly, and so on so forth until it becomes just another memory.
I don't know your situation, but you might want to consider getting a new job.
hmmm, maybe you can't. do you know the 5 stages of grief? i bet you're in one of those phases.
try googling it :)