Hey all my games are really laggy and I can barely even watch youtube videos without it crashing, on witcher 3 LOW settings I get like 15 fps and CSGO medium settings 30. Help please! Specs: http://speccy.piriform.com/results/kdNe7b7GZnuja2ME5Tqj1N7
Uninstall your drivers in control panel and use UDD to remove all left over configs. Then download the newest version again to ensure no corruption to reinstall. Restart your PC. Also note some low setting will offload GPU work to the CPU. Try medium settings. http://www.guru3d.com/files-details/display-driver-uninstaller-download.html
http://www.nvidia.com/Download/index.aspx?lang=en-uk
You have installed a GPU in a prebuilt PC, I wouldn't do that. Your ram speed is slower too, best option would be to build a whole new budget PC at least an i3 6th gen would be best for a 1050Ti.
Custom PC is always the fair choice for gaming GPUs.