Hi, so I just built a brand-spanking-new computer. I have the Windows Vista CD in the drive, I turn it on and... nothing.

The monitor doesn't detect a signal and turns off. The mobo has no on-board video, so I don't know what to do.

Here are the components:

DFI LANPARTY DK X38-T2R LGA 775 Intel X38 ATX Intel Motherboard
HEC ACE-580UB 580W ATX12V Power Supply
Intel Core 2 Duo E8500 Wolfdale 3.16GHz LGA 775 65W Dual-Core Processor
pqi POWER Series 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400)
HITACHI Deskstar 7K1000 HDS721075KLA330 (0A35154) 750GB 7200 RPM SATA
LITE-ON 20X DVD±R DVD Burner With 12X DVD-RAM Write Black SATA
VisionTek 900241 Radeon HD 4850 512MB 256-bit GDDR3 PCI Express

Any suggestions?

Likely incompatible hardware - a good suspect might be your video card/mobo combination. Have a look more online to see if other people have had trouble with your combination. Perhaps someone else here can vouch for his configuration? (or not)

Have you tried booting just the MB + CPU.

It should beep from the speaker and report a RAM Missing signal

Once you get this put in RAM and boot, now you should get a VGA Missing signal

Now add the VGA, see if it boots, if not try a PCI VGA Card.

So on and so forth

I'll try booting with everything disconnected one step at a time like you suggest. The case doesn't have a speaker though, I'm gonna have to figure out how I'll hear that "beep."

UPDATE: I just tried booting with another vid card that I know works (from another computer) and still nada. This leads me to believe it's mobo related.

are you sure you put the card in right? maybe one of the power cables for the card failed. or maybe the card failed all together. try putting it into a computer with a working OS and see if it's the card itself.

Thing you need to check:
1. Check if the CPU is properly seated.
2. Check if the memory is properly seated.
3. Remove all connected parts from PSU except for the motherboard, does the computer turn on? if no, 2 things busted mobo or psu. Check if PSU will work on another known working mobo.

There are lots variables to consider. Just check everything if all fails return it.

HTH

no video usually means a memory problem try using only one stick of memory in DIMM0 if that one doesnt work try another stick again in DIMM0. It might be a bad stick of memory.

Check the FSB of motherboard and microprocessor.