Thanks for all the answers

I know my forum name is confusing. I began with an old GeForce card, but I have a friend who works with computers, and I have borrowed other cards from him. Currently, I am running one AMD Radeon HD 6700 series.

The driver is version 12.104.0.0, from the 13-4 installer. I have been switching drivers back and forth because I have been trying to mine on that card simultaneously with a 4850. No matter what I do, I couldn't get that to work, GUIMiner didn't start, it only got a tray icon that soon disappeared. With some drivers other programs crashed. As I said, I have spent at least six hours and twenty reboots on (not) getting it to work. I think I got all other drivers out before installing the one I just mentioned.

I gave up, at least for now, on that and is now only trying to mine with the 6700 series card.

I don't think the problem is in firewalls or routers, as it works with Phoenix, and worked on my other computer. I don't remember if I tried it when I had only the 4850 in this computer.
Also, I don't think BitcoinPool.com supports Stratum, so it can't be the protocol, as I have tried running OpenCL (poclbm) with BCPool and it still doesn't work.

I couldn't get Stratum Proxy to work on my other computer, but I think I'll try it again on this one.