Playstation 3 HDMI Problem HELP?

My PS3 gets a black screen when i plug in my hdmi cables.... It only does this sometimes.... I try it with the composite cables abd they work perfect but the quality sucks.... How do i get my ps3 to work on hdmi again? Ive already tried the 2 beep and 3 beep resets... Nothins workin -.- help?