In reply to Mazza: The majority of knee problems are caused by weak/ poorly balanced quads. Do some work on these bad boys and you should be able to avoid/ mitigate most problems.
A pop or snap noise isn't too good, though. If your LCL, or any other ligament or tendon had snapped (or in any other way were injured), I'd be surprised if it came right quickly. They don't fix particularly fast.
My advice would be RICE (esp the 'I') as first aid, and do yourself body weight exercises- one legged squats, front and rear lunges and plie lunges. Google these exercises if you don't know what they are.
Also, examine your quads for any sore points- if you've hurt your quads the pain may be referred to the knees. Indeed, the 'tightening' caused by an injured quad can cause the knee to hurt.