Please go to [About This Mac] -> More Info -> System Report -> please check your Boot ROM version like MMxx.xxxx.xxx.
Find the corresponding version from http://support.apple.com/kb/ht1237
E.g. My mac min is MM41.0042.B00, I will downnload this one: MM41.0042.B03 (EFI 1.5).
Run it, fixed the issue.
Besides, if this doesn't help, please downgrade your screen-resolution to 1600*1000.