Ok, this happened before gmod10 came out just do you know, I wanted to get garrys mod really badly so I got a steam account, The source I chose for it was HL2E1, after I did all that credit card stuff and double checked everything, I clicked purchase, so then heres when the fun starts, it opens a new window that says something about a credit card failure, I try the whole thing again, and says the same thing after wards. I then call my credit card company and they said that it came through but there was no charge to my credit card, so I start to think; is steam not accepting my card? a while later I tried paypall, same thing happened.

What was the error message? Have you tried it since then? It could have 'fixed itself' by now.