okay i got me a confusing problem with my monitor

i have 2 comps and when i use my main both the built in vid card and new one i bought wont read 90% of the time...keeps saying no messsage received or what ever... i just turned it on and i came on but if i was to turn it off it may not come back on....its really confusing cuz i thought it was my monitor at 1st but i SWITCHED the 2 around and it WORKED on my old 1 but my main 1 didn't so i thought it was my new vid card... switched ports to my built in videocard and it worked....
moved all STUFF back into place and plugged my main comp back together and used built in port and it didn't work.... thru all the routes it seems that i guess my ports and or video cards are messed up....the new videocard is around 4 months to 5 months old...don't know if that means anything...both comps use windows XP

sorry if this is a bit of a messed up question or a REPEATED one...
any help or input would be great..
You may have a short in your monitor cable. Have you tried another one?thanks the new cable is WORKING....gess i missed a simple thought yet again...blah just moved so haven't had internet for a few weeksAlways check the simple things first.
Glad you got it working