Download for Windows Vista Home Basic - OEM:COA for HP Compaq 6735s

I'm trying to find a download of Windows Vista Home Basic - OEM:COA for an old HP Compaq 6735s so I can reinstall windows. I installed the wrong version with an ISO from USB and now the brightness won't work and there's lots of problems with resolution etc.

I have a valid product key and i know the version from the sticker on the underside but I can't seem to find a download.

Any help would be greatly appreciated.