Hi There!

I am looking for a machine needs to meet the following criteria

i5
16GB Memory
~750GB-1TB Hard Disk
Case (Most any config) and PSU
Basic Graphics are fine. 
DVD Drive

Don't require but can include: 

OS, Keyboard, Mouse, Monitor, Dedicated Graphics

Budget Upto $500. Doesn't need to be new. 

Will be used for running virtual labs.