I have a dell vostro 230 desk top computer and i can log in but after i log in all i get is a black screen what can i do to fix this problem.as i had a virus on my computer so i got the microsoft security essentials and that took care of the problem.i was able to get in the computer but then this morning i got as far as logging in then i get a black scree what actions do i need to do to take care of my problem

You say that the problem occurs when you connect your secondary monitor up either solely, or as primary, but it also occurs when you have only the primary monitor connected Therefore I think the problem is inside your computer box not the monitor or cables.
I'd try another graphics card (the specs I have say the default the graphics is 1024MB NVIDIA GeForce GT220, but then they also say Win 7 Prof - http://www.pc-site.co.uk/reviews/dell-business/dell-vostro-230-mini-tower-desktop-review), either to the built in one (if your m/b has on-board graphics facility), or a different card (which may be the same model). Have a look in the BIOS too.
14.May.214

If your dealing with a black screen on a dell desktop it could mean a couple things. First make sure your monitor is connected to the back of the computer. Second make sure its connected to the right video card because there may be 2 of them. The one at the top is the on board video and a lot of people add a better one in a pci slot towards the bottom. In event that is not the case and the monitor is turned on it could be a faulty video card, bad driver, or the video card needs reseated.
1. turn off computer Sometimes when moving desktops pci cards are jarred and need reseated.
2. Open the case at the back by removing the two screws holding on the side panel
3. then remove the screw that is holding the pci video card, pull out the card
4.then reseat
5.rescrew
6. restart
if this doesn't fix the issue then buy a video card that is compatibly to your motherboard and replace it

if it is an onboard video card buy a pci or pci-e or a video card that is compatible for your computer

wab cam hook up to my desk top

The docs, including the service manual, for the Dell Vostro 238 are at this web page. If you're looking for an actual circuit board schematic, you're probably out of luck. If you need the board layout for jumpers and so forth, the service manual page 28 is for you.

check if u have a RAM problem and if the powersupply is failing

If you are sure the graphics adapter is gone, you have check ALL cables, connections, try another monitor/ cable, drivers: http://www.dell.com/support/drivers/us/en/04/Product/vostro-230. A Graphics card is a option, make sure to look at the min. requirements for the graphic card, the power specs are important. I would not change the BIOS if Dell does not require it.

Check with the LCD by attaching one side to the LCD and other side to the laptop. If display is clear on the LCD then your laptop's screen have some problem otherwise your laptop's motherboard have some problem

maybe it's a motherboard problem

Your computer is toast! If it was submerged in water, your motherboard, hard drive, memory and power supply are contaminated.

If you are running windows:

Click on START
Then SETTINGS
Then go to CONTROL PANEL.
Then POWER OPTIONS.

In the POWER OPTIONS screen you will see the timeout values for your display, hard disk, and standby.

Set them all to NEVER if that's what you want.

Then hit APPLY.
Then OK.

That should be it.
Good luck and please post back if this helps.