the 18 was my only display for 2 years and worked perfectly. i have tried different cables, and tried it on both of the 5770's dvi connections. the issue only came up when i added the 23 and relegated the 18 to secondary. i will look for a reset option when i get home from work tonight.
the more i think about it the more i am beginning to suspect that i am underpowered. when both are in use even the 23 twiches on occasion, but is fine by itself, as is the 18