Device Manager Error 31

Every thing I read about this points to a device driver. When you say the hard drive only works on one channel do you mean one end of the cable or one connector on the main board? Have you tried moving the jumper on the hard drive to master or slave?
Do you know the type or name of the main board you could go to their web site to see if there is a trouble shooting FAQ.

Gonna have to guess here, info is a little mixed:

You say you got zapped, then you got a Device Manager error 31?
that error is "Windows can?t access the drive your drivers are on, so restart."
So I presume this error referred to the existing system drive, the 250GB one?
Then you bought a 300GB drive and are having trouble getting that recognised?
Does BIOS see it?
Can you boot from the old system drive? what symptoms, if you can't? That 31 error?
Finally, you have "multiple drives".... what are they?

Ok, come back on those later please, try the obvious first:
Leave the new drive out of it for now (ie disconnected), let's see what is wrong with the old one:
Boot to last known good configuration (F8 to get the menu when booting, then select)

or
Try a System restore to a point before you got zapped

or
try System file checker, by opening a command prompt window (it's in Accessories) and type
SFC /SCANNOW
(you'll need your installation CD)

or
Go to Device Manager and uninstall your network adapter, reboot and let Windows "find" the new hardware, that should replace the drivers, in case they got corrupted.

Finally, if none of those work, try a non destructive "hot" re-install of XP, Fred Langa tells you how here:

http://tinyurl.com/hutg5

All of these suggestions are made on guessing what you mean in your post, if none seem applicable, please elaborate by commenting back

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Finally, if you get no joy at all with the 250GB system, you can try a clean install on the 300GB drive, but you may have problems with Windows seeing one that large, best to install to a smaller 136GB partition, and change partitioning afterwards.

Leave the old drive out of it, until you have successfully installed, updated etc, then you can slave it to retrieve any data afterwards

Also there are plenty of free disaster/recovery tools about, but try some of these ideas first, and comment back please

I have answered your question about the Device Manager Error code, and you have tried one of the sugestions, WHAT ABOUT THE OTHERS I MENTIONED?
They should either help, or narrow the problem down to an area that can be explored further.

However, here is something else:
It looks to me as if you have a problem with the very large disks here.

If the 300 GB is a virgin one, try using a 98 type start up disk and creating a small partition of around 20GB, install XP there. If you can't use a floppy, there are CD versions to do the equivalent, try bootdisk.com, many others around.

Once in you can use XP itself or one of the many partitioning tools around to resize and/or create new partitions.

To me, all this smells as if it is related to the large size of the drives, have a go at a small partition (<32GB)and see if you can get online, comment back please on what you have tried, the info you provide is still sparse. We need more to be able to guide you.

I have links for the recovery tools, should you need them, but the other suggestions I made and this idea should be enough to get you started.

http://Error31.com - they seem to offer a wide range of solutions to the Error 31 problem - don't know if it's worth anything:
Error 31