unable to use proxies

[firehead]

Up until about a week ago I've been able to use various proxies without any problem. Now, whenever I put the check mark in Microsofts Explorer option box for using a proxy I can't view anything. I always get a 'page cannot be displayed' message. I've tried probably 10 to 20 different proxies from different proxy list web sites. I've tried it on different days too and nothing helps. As soon as I turn the proxy off by taking the check mark out of the box I'm able to surf. I've done everything I know to do. Might my ISP be responsible? Can they block someone from using a proxy?

[DATA]

HELO THERE,
IF THEY DECIDE TO LOOK FOR OPEN SOCKETS ON COMMAN PORTS such as 1080 an 8080-yes if they can find open socket they can block access to it.
how ever if on the proxy 1080 or 8080 are closed ports u may still able to connect through that proxy if u can connect to the proxy on some other port.