Where do the cables go on my dell OptiPlex 280 model GHZ 3.0?

There is no S280 in the Optipex model line, just GX 280 and SX 280.
The problem you are describing is common to the GX 280 model.
Here is a link to the manual:
ftp://ftp.dell.com/Manuals/all-products/esuprt_desktop/esuprt_optiplex_desktop/optiplex-gx280_user%27s%20guide_en-us.pdf
Select "Small Form-Factor Computer" and then select "About Your Computer". Scroll down to "System Board Components".
To the right of the processor is a smaller heat-sink attached to the motherboard via a wire similar to the size of a paper clip bent open. That wire is soldered to the motherboard which may have loosened it's connection and the circuit is open. This heat-sink on the chipset of the motherboard. The wire needs to be re-soldered to the motherboard.

That is your CMOS battery. This keeps the time, date and configurations settings of your computer when you power it it off.

no ... dell optiplex GX280 is a socket LGA478B.. go to www.dell.com... ty

Try . DEL button of F10 those two should work :)

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A USB wireless adapter assuming you have a wireless network available to connect the system. Adapters are generally around $20
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&IsNodeId=1&Description=wireless%20adapter%20usb%20n&bop=And&Order=PRICE&PageSize=20

There's a collection of drivers for the GX280 for Windows 2000 and XP on the Dell website: http://is.gd/ejJcM
If you're running a later version of the operating system (for example a 32 bit version of Windows 7) this webpage might have a solution that will help: http://is.gd/ejJmo (Microsoft Technet community)

You will need to obtain a Dell Windows XP installation CD. Unfortunately, these discs cannot be bought from the local computer store, but you may have luck posting a request on Craigslist.

No additional data cable required !

That slot is actuall not accessable externaly. The open bay is for the AGP slot right next to it. Directly to the left of that slot you have a riser board the provides 2 additional horzontally mounted pci slots. You'll have to use one of these.

You cannot use drr667 on this computer since it only supportr ddr533, and it will be better if you use one stick of 1GIG RAM since your motherboard supports up to 2 GIG of RAM...