I am installing Mint 17.2 on a Dell XPS laptop. It has an nVidia GeForce 8700 GMT chip. I booted with the DVD and had to select 'compatibility' mode to get to the desktop. Then I went to Driver Manager and selected the recommended driver - #340.96 and hit apply.
It seems to have installed it. Then I installed Linux but at reboot the screen simply scrolls through several colors and never displays properly. This is what made me select 'compatibility' with the disc.
Did I miss a step to save the driver, or did I select the wrong one?

You may have Optimus graphics.

Thanks for your reply. The service tag is:9FGW9F1 - just in case you wish to check it at support.dell.com.
The specs page says it is: NVIDIA SLI Dual GeForce 8700MGT with 512 GDDR3 Memory
It is a Windows XP generation laptop and I'm pretty sure it is not Optimus graphics.

I've tried rebooting from the install DVD, and in Driver Manager selected 390-updates driver but no improvement.

Thanks again for you help!

You can't really install drivers using "Driver Manager" during the installation.
That step is done after the install and after first boot.

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I guess it is not Optimus then, but easiest to check it is looking at lspci output, if Intel and nVidia both are listed you have Optimus.

Problem solved. I found this advice to edit the grub as follows:
Go to the line starting with the word linux and ending with the words: quiet splash
Add one of the following '????.modeset=0' parameter at the end of the long grub command line as is (type 1 space before). Use the parameter related to the brand or chipset of your video card . pe.: use nouveau or nvidia for nvidia based cards (proprietary driver, just nv in some linux distributions, nouveau driver is the default in Mint) ), use radeon for amd/ati cards, i915 for intel based motherboards, ,,, These are the most common examples.
nvidia.modeset=0
nouveau.modeset=0
radeon.modeset=0
i915.modeset=0
r128.modeset=0 (for very old ati rage 128 cards...)
If you don't know the brand you may use just one word: nomodeset

I selected nouveau.modeset=0 and rebooted. Got into the desktop and then used Driver manager to install the recommended nvidia driver. TA-DA!

Thank you Emerson and Habitual for you assistance!

Glad it worked out and Good Job and Well Done!