Assuming you have an Nvidia GPU;
First thing you have to do is reinstall graphics drivers, its unlikely but possible that your drivers became outdated in the short time you were away.
Here is a video tutorial if you need a walkthrough:
https://www.youtube.com/watch?v=LQ7lF-rrJrA
Next, tell your graphics card to run at full power:
To change this setting, with your mouse, right-click over the Windows desktop and select "NVIDIA Control Panel"
-> from the NVIDIA Control Panel, select the "Manage 3D settings" from the left column
-> click on the Power management mode drop down box and select "Prefer Maximum Performance"
You should also tell your cpu that it is allowed to use full power by going into Control Panel under the Power Options and setting it to High Performance.
*Both these tweaks are safe and are NOT overclocking*
Doing these three steps will boost your performance, your computer will be running at it's full potential.
Hope this helps, good luck.