I had this problem with my nanna's laptop that she somehow screwed enough to warrant re-doing the whole system.
Had to format the whole system and download a full copy of windows 7 and use the key that was underneath her laptop to fix it. Before that I tried to go back to vista or xp however install there was something missing that made it go into infinite restart loop.

I'm just wondering which shop you took it to that'll charge you $300+ for that problem!?

ive had problems like this with my desktop computer, i solved it by giving the computer to my brother and buying a mac

Always best to format before installing an operating system. Weeds out any bugs.

Interesting that your Win7 upgrade key worked with a Win7 full install from scratch... how did that work?

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MY99 WRX sedan WRC blue Sold :(
MY99 WRX sedan Dark blue pearl :D
MY97 Liberty Outback Ltd Wagon
1990 Mk3 Supra turbo fully rebuilt 7M-GTE (Older son)
1991 Celica GT4 (Younger son)

The product key must be universal over upgrades and fresh installs?

Still can't believe I was told about $300 for a job that would take me a couple of minutes to do if I had to again. I guess my explanation can't have been great, but it's pretty steep for a quick job...

Yeh, but an upgrade disk costs a fair bit less than the full version...

Ah never mind - at least you're up and running now

__________________
MY99 WRX sedan WRC blue Sold :(
MY99 WRX sedan Dark blue pearl :D
MY97 Liberty Outback Ltd Wagon
1990 Mk3 Supra turbo fully rebuilt 7M-GTE (Older son)
1991 Celica GT4 (Younger son)