black screen on monitor Dell Dimension 5150

@bk555 the 4th light off is a generic error message:

Another failure has occurred.

• Ensure that the cables are properly connected to the system board from the hard drive, CD drive, and DVD drive.

• If there is an error message on your screen identifying a problem with a device (such as the floppy drive or hard drive), check the device to make sure it is functioning properly.

• The operating system is attempting to boot from a device (such as the floppy drive or hard drive); check system setup to make sure the boot sequence is correct for the devices installed on your computer.

I'd start with checking to see if you can access the BIOS. It is possible that you drive may have failed.See if you can run the Dell Diagnostics

1 Turn on (or restart) your computer.

2 When the DELL™ logo appears, press <F12> immediately.If you wait too long and the operating system logo appears, continue to wait until you see the Microsoft® Windows® desktop. Then shut down your computer and try again.

3 When the boot device list appears, highlight Boot to Utility Partition and press <Enter>.

4 When the Dell Diagnostics Main Menu appears, select the test you want to run.

Let us know what you get.