Issue With Running Games On Dell Optiplex 790

I have a Dell Optiplex 790 Desktop with 16GB of RAM, a 3rd generation i5 Processor, no GPU.
I just got this desktop and I love how smoothly it runs just about every process, but for whatever reason gaming runs absolutely atrociously. For reference, before getting this desktop I was using an HP Laptop with 8GB of RAM and while it didn't handle programs as smoothly, it handled gaming much better. 
I've tried updating my drivers, to no avail. I can't really help but feel this isn't a hardware issue- I understand that the computer's specifications aren't exactly ideal for gaming but it seems strange that it's outpaced by my old laptop. Any help would be massively appreciated.