I am building a new gaming computer, and when I turn it on, it does not POST. Specs: Case: - Antec Three Hundred ATX Mid Tower Case Motherboard: - Intel DP45SG Extreme Series P45 ATX LGA775 Power Supply: - Corsair 650W TX Series PSU Graphics Card: - Sapphire Radeon Toxic HD 5850 1 GB Processor: - Intel Core 2 Quad Q8200 2.33GHz Memory: - OCZ 4GB (2 x 2GB) PC3-1066 DDR3 1333MHz Monitor: - Asus 23 inch LED monitor Details: When I turn on my computer, all of the fans run and the LEDs light up, but there is no POST, or at least no display (the monitor displays, "No signal"). Soon after I turn on my computer, there is a very short, high-pitched beep, then about four seconds afterward, a long (about half a second), low-pitched beep. I'd assume this was the POST beep, but it sounded odd to me (the first beep was significantly louder than the second beep, and the time between each beep was long). Additionally, when I remove one (of two) of my RAM sticks, and then turn on my computer, there are three consecutive medium-pitch, medium-duration beeps that sound different from the other ones. Everything seems to work fine; the inside of the computer looks as if it's working correctly. I have tried using every port on my graphics card (two DVIs, one HDMI), but the results are always the same (no signal). I have the 24-pin and 4-pin power plugs plugged in correctly and the molex connectors in the graphics card. My motherboard has no on-board video, and I cannot swap out parts to troubleshoot because I have no other compatible parts.