Trouble with external monitor waking connected to MacBookPro


For years I've used my macBook Pro connected to an external monitor. I would hit the spacebar or mouse and the monitor would wake up. Then I set the MacBookPro to require it to instantly go into a more secure mode that requires me to enter the password upon waking. Still, everything worked fine. Recently I have had difficulty with the monitor waking from sleep mode. I have to turn the monitor on and off a couple times (I have the instantly require password mode set as well) to get the password window to come up. This started, then the next snag has been the MacBookPro won't wake up by lifting the lid either, which leads to rebooting etc. The latest is the monitor sort of come up for a second, I could see the screen for a split second, then black.

I fiddled a little with the "show displays," checked the DVI cable, did the usual jiggling, plug/unplug and last night, fed up, I just unplugged everything over night.

Plugged everything back in this morning, and though I still had a bit of trouble coming up with the sequence to get the monitor awake, I'm using it right now, and actually the computer seems to be actually performing better (I had to run disk utility the other day because there seemed to be lots of resources being used, slow sluggish performance, that sort of thing). The screen actually seems to be finer...

Could all this just be a cable going bad? Of the little DVI connector from the MacBookPro to the cable? It seems to have some strain on it from the computer as the macbookpro is sitting on an iCurve (yes, I had one of the originals.... very cool actually) to raise the laptop off the desk and allow air circulation, but I'm wondering the connection has gotten a little worn over the past 5 years.

The monitor is an ASUS VK248 and I actually have had warranty work done on it before.

Any thoughts other than immediate replacement of the most expensive parts :)
I left the monitor unplugged from the laptop all night; fired up the laptop out of sleep, then plugged in the dvi and it worked fine. Once the computer went to sleep, again, however, I was unable to awaken the monitor even with repeated plugging in out, etc. I think carefully tightened the dvi cable as tight as possible and then propped the dvi adapter up so the connection isn't pulling down on from the computer from gravity BANG. The monitor came back up! I have another dvi adapter I can test. I'm hoping it's not the actual connection TO the computer because then we're at hit or miss for sure. Thanks.
The end of the story: I packaged up the monitor, sent it back to Asus for repair (again, last time for a shadow in the lower left corner in Jan), waited 6 days for it to arrive. They repaired it. Waited 6 days for it's return. It appears they replaced the cable. They don't say what, if anything else, they did. So, probably was just the cable. I had a 2002 20" cinema display I keep for backup in the basement during the interim. I forget what a good little display it is ... thanks for your input.