500 server error

I get this error when I try accessing random websites.

Server Error
The following error occurred:

[code=SERVER_RESPONSE_CLOSE] The server closed the connection while reading the response. Contact your system administrator.
Please contact the administrator.

Ive tried everything, even some of the help on google search wasnt helpfull at all. If anyone knows of how to fix this problem it would be greatly appreciated.

Im on a pc and using a dial up connection and using firefox. It happens randomly so sometimes it works and other times it doesnt.

thanks