Hi, Firstly I would not accept what this shop has done for you. They don't seem reliable at all and I would insist they really fix it. without any more money to them!
On drivers, Windows Update often is behind and reports them as up to date when they aren't. The HDMI audio comes from your graphics card, nVIDIA and Realtek is built in your motherboard.
Anyway, if you are getting lines on the monitor I think the new GPU may be junk.
Your BIOS is dated, visit the board's web page to see if there is a newer one, there may not be but worth a check. Also the same for the GPU, use nVIDIA's site NVIDIA Driver Downloads - Advanced Search
and follow this:
Try these steps to install only
the graphics driver.
1.Download the preferred driver and save it to the desktop.
2.Double click the installer and you will see a screen where it will be extracted to, change that to your desktop.
3.Open Device Manager through Control Panel.
4.Expand Display adapters and right click the name for yours and choose Update Driver\Browse my Computer. Select the driver folder you just saved on the desktop. Click Next.
5. Your system should say "Windows has successfully updated your driver software".
If you get a window saying you already have the most current driver, go back to step 4 and choose Uninstall Driver software instead. Then restart from step 3. Attachment 228491 Attachment 228492