PC don't start

my PC has Windows XP and was working good and I try to fix a diferent HD wiht my PC, so I decide for take my HD out and put the other HD and I didn't fix the other HD, so I put my HD back and that is when the PC did'n start

 

Put out cell of main board and install new data cable it will work if not go to conputer hardware shop and do not touch antthing or you will sorry.ALso cheque your hardisk if it is making noise it is finished install new hard disk.,

 

Personally I would bet on a loose cable or some other device. Go through your computer and make sure everything is seated (things like drive cables, video cards, whatnot). Doublecheck your drive cable to be sure you put it back in the correct slot.

This second hard drive you tried out, was it a known good device, or were you trying it out to see if it worked?

 

And just to add what Bill has advised it is possible with some ribbons to have connected it upside down at the hard drive end.