Do what Rival said looks like it great info. If that doesnt work, make sure that your not running to many Programs to help free up some CPu time for the game. A few years back i had this problem where i wold get VERY VERY low FPS like what is happening to you, but my ping was the same as normal. I found out that i was having Hardware Interrupts.

(Hardware interrupts occur when a peripheral wants attention from the CPU, High CPU consumption by these activities can indicate a hardware problem or device driver bug.)

This makes it so that your CPU is being held up and you cant use the CPU time for anything else. Look in your Task Manager and see if you can find anything that says "Hardware Interrupts".