OK. I thought I'd wait and see if anyone else answered this. But you are in a real hurry so, I'll give you what I have done and then what I have seen posted here as well (just in case what I have done didn't work). I will not be responsible for any damage to your hardware.
Don't know what have you tried so far, so I'll suggest that you run Envy and install the latest driver for you nvidia graphics if you haven't. If that didn't do it, then you may want to know what your current settings are. It's not necessary but it's good information for later if none of this works. Open a terminal and enter:
Make note of the pop-up warning. When you select the cancel button on this pop-up window the window with the current sync rate data will close, so you may want to write them down for comparison later.
Next run the following command in a terminal:
sudo dpkg-reconfigure xserver-xorg --frontend=gnome
This will start a configuration session that will ask questions that will be used to reconfigure your user settings. When this completes and you reboot you should have settings that look good. If not then you will want to do what others have done. Manually edit the refresh rates in the xorg.conf file. It is located at: /etc/X11/xorg.conf
To do this start by entering the following in a terminal:
sudo gedit /etc/X11/xorg.conf
When the text editor opens the file scroll down to Section "Monitor"
It will have something like:
Identifier "Name of your monitor or Generic Monitor"
You want to add Horizsync and vertrefresh after the line starting with Option. For example you would have something like this:
Identifier "Generic Monitor"
Horizsync 30-70 (what your hardware specification specifies)
Vertrefresh 50-160 (what your hardware specification specifies)
Please note the values you put here for Horizsync and Vertrefresh should match your monitor specifications. I will not be responsible for any damage to your hardware.
I hope you are successful and you enjoy Linux Mint.