dell d600 will not power up, only middle led(caplock) flashes?

It does power up, but stop on some hardware isue.
Try doing a search on "flash code"

I got that link from www.dell.com with a search for "flash code":
http://support.dell.com/support/topics/global.aspx/support/kcs/document?c=us&cs=19&docid=54768&doclang=en&l=en&s=dhs
Title: Portable LED Diagnostic Code Information - Technical Assistance Bulletin (TAB) - 131642

The page lists your model.
The middle LED flashing suggest a memory isue, probably a memory module that need to be reseated or replaced.
Reseating process:
Be sure to remove the battery and disconnect the power.
Open the case or, if you are lucky, an access pannel. Then, you remove the memory module(s) and place it back in the same location.
Close everything, reconnect and power up.
If the memory is bad and need to be replaced, take the oportunity to upgrade it as much as possible.

If reseating or replacing the memory don't solve your problem, then you have a failing memory controller. It's a part of the BIOS/motherboard that can't be repared, meaning that you need a new computer.

Electro
May 2012