I would start by giving just a bit more information, like what video card you are trying to run and what driver do you have installed, which "miner" are you trying to run in guiminer, what pool are you trying to connect to, etc.

It is likely that all the above are kerfuffled and kerplugeoned, I would start by verifying the pool information - miner/worker user password, correct IP/port for mining (not stratum mining), etc.

Google gave me over 400 results for site:bitcointalk.org "No JSON object could be decoded"