Can somebody tell me the steps to setting my external hard drive to default?

Question

My computer is a dell dimension 4600c

Answer 1

Turn on (or restart) your computer.

When the blue DELL™ logo appears, press 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.

Go to "Boot Sequence" & press "enter".
Choose what you want to be the first boot device from there.

Source :
Dell™ Dimension™ 4600C Service Manual
System Setup Program
http://support.dell.com/support/edocs/systems/dim4600C/sm/syssetup.htm#1104309

*** like the first answer pointed out ... you much have Windows (or a utility with bootable system files) installed on the drive or it will not boot from it.

regards,
Philip T

Answer 2

Boot into BIOS and set it to start external HDD first. You need to have the OS installed on it though or you cant boot it. To boot into the BIOS, you just rapidly press delete when you bootup the computer. Make sure you dont change anything else though or you may not be able to fix it yourself.