Okay, so my videos that I play both on and off the internet have been lagging MAJORLY.

I went through deleting unused programs to speed up my computer a few weeks ago so I think I deleted a necessary program.

I made sure I had Adobe Flash Player, but what are the other necessary programs to have for videos to run smoothly?

I need to make sure I have them all.

OR if this is not the problem, any other suggestions?

My computer runs great and fine, I have DSL, it's fast as usual, so it can't be the speed of the computer..

to PCHF.

Here a couple of things you can do to help your computer.

1.
Download http://www.ccleaner.com/download
It's free, though they do accept donations.
Along the left side of the window, you want to first select Cleaner.
Analyze, then run.
Next, select Issues.
Scan, then fix.

2.
Defrag your drive(s).
You can do this from the Properties >> Tool tab on each hard drive.

3.
Is your video card driver up to date?
If you provide the version of Windows you are using and the make/model of your video card, I try to find you a source for the latest driver for your video card.

After taking these steps, let us know how your videos are running.

Good Luck...