I have a T60 and have somewhat similar issues.
A while ago, the when resuming from sleep, the laptop would do just as you described. Everything would turn on ok, but the screen would stay blank. HDD, cpu fan both were running.
Now, the laptop takes about three minutes to display the screen when resuming from sleep. I open the laptop, everything turns on ok, but no display. Wait 3 minutes, display works!
I have two suggestions. First, when the display is blank, press Fn+F7, which changes the display output. Press it one switches to VGA out only, twice goes to VGA out and the LCD. Pressing it twice sometimes made my display work again.
Who knows why. (You can always press it again to return to normal) My second suggestion is to simply wait. When the blank screen appears, give it 10 minutes. If its still blank then it's safe to assume it's not gonna do anything.
I think the root of the issue lies within the ATI display driver. I think it has a conflict with sleep. I don't think updating the driver makes a difference either. I doubt the newer drivers have a fix for this model..... I have a friend who can't put his desktop to sleep because of the ATI driver. Connection? Possibly. Hope this helps.