I bought Acer 7535g laptop Dec 09.
It was fine, worked great, came with Windows Vista Home Premium, no problems.
It also came with 'free' Windows 7 upgrade. Great, I'll have a new laptop, with new Windows 7! Paid £7 for the postage and did it.
Since installing, learned that because the laptop runs off of a HD 4570 for more intense work, and a low powered HD 3200. Windows 7 doesn't recognise this, and refused to let me do anything, would often boot up using the 4500 and therefore have no display. I tried installing, deleting ,reinstalling drivers for both cards, nothing, it's a recognised glitch.
So I thought screw this, I'll go back to Vista...
Borrowed my mates Vista Home Premium disc, as my laptop didn't come with one. Installed, put my Windows Serial Number (stuck to the bottom of my laptop), in, invalid. Again, invalid, tried over, invalid.
Here's the problem. I was invalid for so long that I've been locked out of Windows Vista, have no code to use and can't get the Windows 7 disc to boot up either.
I called Windows, they said you can't go back from Windows 7 to Vista, and I should call Acer to get a new Windows copy. I called Acer, they said there's nothing I can do except buy another copy of Windows, (from what I could get through to this Indian guy who spoke awful English).