red light when i turn it on

when i turn my camera on to take pictures it has a red light shouldnt it be a green light and my screen is black so what should i do

Sounds alot like the faulty CCD issue that Canon and other camera makers dealt with a few years back. Sadly though, the S2 isn't on the list of affected models so it's unlikely you'll be able to have it replaced on Canon's dime. Here's how somone with a simliar problem dealt with Canon on it:

Here's an update to the failure of the Canon S2 IS, the CCD is bad as reported to me by Canon and they want $120.00 plus shipping for the repair. After arguing with them they reduced the repair price 20%. Consumers BEWARE this cameera has problems like the other models that use the Sony CCD, but they won't admitt it. I also understand the S3IS is affected with the same type of problem. I would suggest anyone buying one of these models to buy the Store extended warranty with replacement.

The user goes on to say that while Canon ended up promising him an upgraded S3IS in the end, they sent him back his S2 fully repaired. Probably at his cost.

The thing you have to ask yourself is, would it be worth the cost to repair. Rule of thumb is that if it costs 50% or more of the sale price to fix it, you're much better off getting a new one that will give you more bang for the buck.