Hello and welcome to Bleepingcomputer!
I see that your problem just popped up out of no-where.
When I see posts such as yours, the first thing that comes to mind is a faulty connection, one that happens intermittently, sometimes it does, sometimes it doesn't.
Before I proceed with instructions for you to follow, I have to post an important warning:Warning: Before proceeding with any attempts to repair or modify the inside of any computer, be sure to ground yourself to the computer's metal case before and at all times while you are performing this task.
The human body is capable of storing lethal amounts of static electricity, which is capable of destroying the sensitive electronic components which are located inside a computer.
First, over time air/humidity can cause oxidation to build up on the metal surfaces that mate together to form the connections between the components and peripherals located inside the computer case.
The key is to disturb this oxidation. This can be done, by simply going through the computer and disconnecting and reconnecting all the wires which are plugged into the various plugs inside the computer case.
Examples are: Any or all power supply wiring harnesses that go to devices such as hard drives and optical drives.
The ones that go from the PSU to the motherboard, there might be both a 4 pin and a 20 pin connector.
The wires going to hard drives for data transfer, this is the case for both the E-IDE/PATA ribbon wire or the SATA hard drive data transfer wire.
Remove and return any add-on cards such as Video cards, sound cards, modems, ethernet cards from their slots.
Remove the RAM sticks and return them into their slots again.
Anything you remove, please make sure it is fully seated, fully connected to its mating surface!
Please before restarting the computer, make sure everything looks like its supposed to, make sure none of the plugs or cards are loose or out of place and are firmly making conntact with their mating surfaces.
Make sure no wires make contact with cooling fans stopping them from spinning as they should.
I can make this a long list, however I think you can get my point by me just saying, go through the computer case and un-plug and re-plug any and all wires which are plugged into something.
Doing this procedure disturbs the oxidation build-up and removes the intermittent connection problem, which eventually will get worse over time so there is no connection at all.
After you try this, please come back to this forum after a test run and let me know if this problem has gone away.
Edited by MrBruce1959, 29 May 2010 - 01:09 PM.