Odd Problem with Laptop HDD

Hi,

I've been fixing a few peoples laptops lately and all has been going relatively well, I'm a bit stumped on one particular one though and was hoping maybe someone would be kind enough to shed some light on the situation, i'm going to have to return the laptop un-repaired it seems, but it'd be nice to have more info to pass on.

Lady has a Sony Vaio. Thing boots up ok, but as soon as you go to do anything (even open IE and browse to web page) it grinds to a halt and programs crash. I deleted some programs, amended startup options, ran virus/spyware scans, booted in safe mode, did a windows repair but nothing seemed to fix it. So, with her permission I offered to wipe the hdd and reinstall windows from scratch to see if it'd solve the problem. I couldn't get the damn thing to format from within her laptop, so took the hdd out, put it in my test laptop, formatted the drive and returned it to it's original home... only now the laptop wont recognise the hdd, at all. I replaced it several times to make sure not doing it wrong and tried another hdd in the laptop which was found but wouldn't boot the windows install on the drive. I figured I may have damaged the HDD whilst moving it so ordered in replacement, that wont find either - but having now checked both her old one and the new one are found on my other 2 laptops... and my hdd is found on hers but wont allow to boot.

Does it sound like the mobo on the laptop is gone or am I missing something here?