Why isn't my VGA cable working?

Why isn't my VGA cable not working for my PC all of a sudden?

• Okay, so yesterday I went on about cleaning my whole desk full of dust and un-pluggged everything on my desktop setup. Anyways, when I went to go plug everythingback in, I find my monitor isn't showing my regular computer display. The power seems to be working fine since it shows a yellow light all the time, but it always says monitor going to sleep. I have a HP a1720n with a Raedon HD 4600 or something along those lines. Anyways, I tried to swap the both ends of the cable from PC to monitor and from monitor to PC but nothing seems to work. I tried plugging it in with my laptop and it seems to correctly display information from the laptop to my monitor. What could be the problem? My monitor only has 4 outputs which only 3 of them I use. The power cable, The VGA cable, and the Audio In/Out [the monitor has built-in speakers] Everytime I turn it on it says monitor going to sleep. No DVI or VGA input, but it doesn't need a DVI. However, when I unplug the VGA from either the monitor or the hardrive, it says Check Video Cable, so I'm under the impression, it's able to pick up a connection, but can't use it properly? What can I do?

• Answer:

  Check that you don't have two VGA connectors on your PC. If you do (one motherboard, one expansion card), make sure you are plugging into the right one... Otherwise, it seems like the video card is not putting out any signal. Check the video card, how well it is seated in the motherboard, and check if it requires any extra power connectors (6 pin PCI-E)