Inspiron One 19T Horror story

I sold a friend of mine my Inspiron One 19T desktop a week ago, and less than 7 days later he "Fixed" it. It was working fine, and when I dropped it off he told me he wanted to "tether it" to a 2+ year old HP Laptop to transfer programs, because he had seen some guy do it on YouTube that looked like he really knew what he was doing.  The Dell ha(d)s an Inspiron Dual Core 64 processor, the HP has a 32 AMD processor.  He began the transfer and when the computer crashed (As I warned him no less than THREE times that it would) he could not find the restore DVD and restore discs that Dell sent with the computer, so he just put in the restore disc from.... his HP laptop.  You can imagine what the result was from that... He said that I never gave him the disc, then when I reminded him I did he said that he forgot.  Then when he put the disc in after 45 minutes, it asked him if he wanted to Restore, (R) or Format(F).  And he chose format.   He called me up and told me what he did, and I told him to get the DVD I gave him, but of course that no longer works and neither do the restore discs from Dell that were sent with the computer less than a year ago.  He tells me that Dell cannot determine what kind of computer he has, but he has downloaded drivers from Dell.  He keeps on insisting that it is all my fault, because I did not make a second DVD even though it was not required.  He also cannot understand that when HE formatted the hard drive and installed all those HP programs he pretty much ruined the computer.  It went from a 64 bit processor, to a 32 and from a 360G hard drive to a 280 (Just like the HP laptop.)

My question is can someone from Dell even tell me that this is repairable?  He refuses to tell the techs what he did, so there is no way that they will know how this happened.  I feel bad because I sold him this computer for 150.00 it was working perfectly and he has done all this and wants me to fix it.  I'm going to buy it back, and just want to know if it can be fixed, or if I should just part it out and get rid of it.