Sound but no picture?...

Hi

I havent seen this one crop up in any threads so far. Sometimes my XBOX 360 starts up with only sound (no picture). One green light on console, no reds.

Changing cables doesnt make any difference. Checked for loose cable connections in back of TV and XBOX and all fine. I've used th etowel trick about 4 times now to 'reset' the XBOX and this works but it now a matter of days before the same problem arises, and I dont want to keep diong th etowel trick in case it makes matters worse.

Will re-doing the Heatsinks with Thermal compound be a worthwhile venture for this problem?

Thanks in advance for any useful advice...