Dual monitors problem with 10.7.4

I upgraded to lion last week.

When I plug my laptop into my external monitor, the screen on my laptop goes black. I clicked detect display in system preferences, but its not detected.

I got a message at one point that I only had one monitor connected. I can not reproduce this message. I was using spotlight searching for help.

If I disconnect the external display, the laptop comes back on.

I want the extended display not mirror mode. It worked under 10.6. I checked google and searched here, but I couldn't findhelp. Any ideas?

Well the monitor just started working after a third reboot. Its not the cables as I tested those on another macbook.