You haven't included enough details for anyone to figure out the answer. The first step you should take is to isolate the problem - is it in the PS3, the TV, or the cable? Or in the TV selection of input - have you made sure that the correct input is selected?
If you have another device that has HDMI output, hook it to the TV with the same cable and port that the PS3 is now using. If everything works, the problem is in the PS3. If not, try a different cable. If everything works now, the problem is in the cable.
If your TV has more than one HDMI input, try the PS3 on a different HDMI port. The point of all this switching around is to tell which component the fault is in. Oh, will the PS3 work using any other output method (if it has outputs other than HDMI, that is)?