I have an Iomega 500gb Minimax Desktop, and need a new power supply unit, is the center pin + or -

Jim, take he hard drive with you to a electronics shop and let them match it up to a universal power supply/adapter.
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try getting a new power cord from iomega, If that doesn;t work, the drive is probably corrupted. They are under a year warranty. You ship yours to them and they will send you a new one. Try the free chat on Iomega

give it to the service center for replacement and dont tell them u have dropped it or els they wont replace

Take the computer to a qualified Apple technician -- the hard-drive could have "died". Is the drive still under warranty? If so, you can get a replacement for free, but you will need to contact a "Data Recovery Service" if you want to "recover" any of your files.

The boot info is bad. If there is info that is needed you will have to use a recovery program like getdataback fat 32 and getdatabackntfs

if it's 6 months old, you should be still having warranty, suggest you take it back to where you bought it from.

connect your harddisk to computer.
Then right click on my computer icon then click on "Manage"
then click on "Disk Management"

then find your removable device then you find unpartitioned space create new partition .then check.

Also check jumper settings of your harddisk.
It should not be on 16 bit or 32 bit in hardisk.

In your situation I would :

open the minimax enclosure, and take the hd out, (just open the enclosure, not the hd itself), and then open your desktop and connect this hd as slave (I am guessing you have a desktop with IDE hd and that the minimax has an IDE hard drive in it.... or both your desktop and the minimax has SATA hard drives) and then when you turn on your computer you should be able to see your second hd as a partition and be able to see the info in there, yet if windows does not recognize it, that means your hd is useless., yet remember you have to change the pin on your external hd to be slave or auto detect, if you let it as master your computer won't boot, bout do not worry, after you unpluges the hd from your desktop everything will be normal

p.d.
shutdown and unpluged the power cord from your desktop when adding/removing the hd.

Yes. The MiniMax is designed to match the MacMini from Apple and comes formatted out of the box to work with a Mac. (One of the few drives that is!)
I think Iomega supply various Windows drivers on the CD

I just connected a new power supply to my zip 250MB, with the center pin as positive - and it worked out well :-)