|The Dell Studio hybrid 140g desktop uses an external power supply. Is it plugged into the computer?|
People frequently pull on the cord instead of pulling on the plug when they unplug an external power adapter.
The plug on the end of the cord that plugs into the computer may be damaged, or the cord near the plug may be damaged. In that case, you may be able to fix your problem by chopping off the end of the cord there and replacing and wiring up the plug.
Or the adapter may have fried for some other reason.
Here's an example of what you need if the power adapter is dead: