What have I done!

[cropwell]

If you have tried on another PC then you have elimnated the PC and it should have worked so this suggests you have other issues.?
Doesn't matter if PC was old, infact often better being old as the PP will be 5V not 3v.

I would start again removing anything that isn't required and re wire. Then Fresh install of software on Fresh PC if possible.
If still giving trouble then chances are you have damaged chips or something on the control board.

In this Case I would just scrap the whole lot and replace with modern gear.

The only chips on the control board are the drivers. If the input stages are bolloxed then I personally would go with the last idea as the PC seems to be very vulnerable. Case and power supply seem OK though although the case may be a little small for 4 drivers.

Cheers,

Rob