Vista - Another Multiple monitor issue

Hi,
I have had my laptop (DELL XPS16) connected to an external display (32" LCD TV) via HDMI cable, and it was working fine when I had it as a mirror (both screens the same).
I wanted to change the settings so I could use the TV as the primary display when connected, so attempted to change the settings i evidently did something wrong, now it won't work at all, additionally when i plug the HDMI cable into the PC the monitor just starts flicking on and off and won't display anything on the TV.
Is there a way i can make the computer 'forget' the TV so if I reconnect it, it can go through the new display wizard again to start afresh?

Any ideas guys? I've trawled the net for ages trying to find a soultion but am not getting anything helpful... basically I'd like to reset my display settings so it can re-detect a new monitor and things would be lovely....

Does the laptop have an external monitor function key shortcut? ie Fn+F4

Where are you setting the monitor up? ie In Vista control panel, nvidia control panel (nvidia card) or Catalyst Control Center (ATI)

It sounds like the resolution may be set to something the TV can't handle. Try setting the laptop resolution to the tv's resolution.

If that doesn't work, try re-installing your drivers.