Changes in 5.4 drivers to 5.5beta drivers fixed my problem
 

I notice several people on here have had issues with the monitors not showing up, etc.

I am running Windows 7 64xbit Home with ATi 10.7 driver (5 series notebook card). Initially when I installed everything it went good. I have two ArcView USB-to-DVI converters hooked directly to the laptop. I have a targus port replicator handling my printer, mouse, speakers, scanner.

the very next day, only one monitor came on. The other unit and monitor were blank and did not show up in display settings. The green light wasn't lit up on the arkview unit but it showed that it was connected in the devices (both of them). The next couple of days went random, none of the cards would work or only one would light up.

Today I upgraded to 5.5 beta drivers and still had a similar issue but I unplugged the unit that was lit up and swapped it with the other one that was unlit (swapped the physical units, not the cables or usb ports). It then installed it and they were both lit up and working perfectly. I also plugged both of them into the targus port replicator, this seem to work better.

I've shut down and rebooted, unplugged the port replicator, came back, plugged it in. Everything is working good so far. hope this helps some of those having issues.