|Did you do any troubleshooting or did you just assume the PSU was bad? Hopefully you didn't order a replacement thru Dell? You could have gotten a 400W Corsair from newegg for about $35.|
"is it possible to boot from the sata hd on the new pc thereby showing the "desktop" as it was on my old pc ?"
No. You would have to boot into the eMachines as usual, then plug in the external HDD. It will be like using a large capacity thumbdrive...you will have to browse thru all the files & folders looking for whatever it is you need.