Sometimes I absolutely can not get my DVD player to play a DVD. I can usually get the DVD to play on my computer but I much prefer to watch it on the TV. Any suggestions?

What region DVD gives you problems?
If your player is multi-region,and the disc still does zip,then it could be a player fault.If the player is'nt multi-region,then make sure the disc is the correct one.In the US,and Canada,discs are Region 1.Here in the UK,it's Region 2.As you know,putting a region 1 disc,into a region 2 player won't work,or vise-versa.
Before purchase,always look at the region code on the disc box to avoid any home disappointment.
If the disc plays on your PC,what region have you got it set at.You usually only get to make about five changes,before it "locks" on that setting,so always choose carefully.
Also,try a dvd laser-head cleaner,which you can get from all good stores.This might also help on your player.

I think you mean your stand-alone home theater type of DVD player...

Are these commercial DVDs, or burned copies of things you've made? Burned DVD media can be quite picky. Certain brands may not play of certain manufacturer's DVDs.

Commercial DVD's should be fine though. If you have determined the DVD's are okay, that just leaves the hardware. Your DVD player might be on the way out.

If you get some compressed air - Open the tray and blow out any dust you can from inside the player. Dust on the lens will hamper the player from reading the DVD.