Can't run the game, can't update laptop drivers (4670), need help

[Finzy]

First of all, laptop specs (Acer Aspire 8935G):

- Intel Core 2 Duo T6600 2.2 Ghz
- 4 GB RAM
- Ati Mobility Radeon HD 4670 1 GB
- Windows 7 Home Premium 64 bit

I've been trying to get Amnesia: The Dark Descent running on my laptop, and apparently it needs updated drivers to run. Everytime I start it I get no display, just the game running in taskbar with occasionally some audio as well, and the cursor gets stuck in the top left corner of the screen. Switching to the game has no effect and my cursor is permanently stuck until I kill the process with the task manager. However, despite following the instructions here and running the mobility modder, the generic ati mobility drivers simply refuse to install for me, saying that my hardware is unsupported. After I click install after choosing express or custom installation (and selecting the package to install if custom), the setup just ends instantly and gives me a yellow error sign - with no actual errors in the error report.

Shouldn't the mobility modder take care of that? I downloaded the latest drivers from the ati homepage as usual, and the readme says that it does support Mobility 4600 series as a "reference driver", and Acer laptops are supposed to work. Now I don't really know what to do. I uninstalled the default laptop drivers and right now it's got no videocard drivers installed. I tried updating them before once by running a clean install with DriverSweeper, but that ended up messing up the display so badly and making it not boot at all that I had to do a reformat, so I wouldn't really like to use a driver cleaner if I can avoid it...

Everything else works just fine with the default laptop drivers, but I wouldn't like to waste my money as I bought the game off Steam. And I heard the default drivers are pretty crappy anyway.

Help would be appreciated.

(I posted this same thread basically on Guru3D if anyone's wondering)

EDIT: Apparently I can't even install the default drivers back anymore, I keep getting the same error (which doesn't even mention anything). Can I do a windows repair or do I have to reformat everything again? :/

EDIT #2: Forgot to mention this laptop has switchable graphics (for low power consumption) - right now it seems to be running on an integrated intel graphics chip. Does anyone know how I can make it switch back to the Ati side, if it's even possible, or if I can attempt installing the drivers in safe mode? And can I control which graphics are used via BIOS for instance, in case it fails to get display on the Ati card?