Windows 7 HP 64 bit won't play dvds in WMC

I am having problems with Windows Media Center being recognized in my computer...I am having to use an external disc player to play dvd's. Cd's play fine, I am able to use my built in disc drive (in the tower/box), but I have no idea as to why it has stopped recognizing dvd's and not allowing Windows Media Center to play them, it used to.
I can use Windows Media Player for ripping an burning music, etc. but not WMC! Can anyone knowledgeable help?

I am not all that advanced in tech. matters..so be gentle. lol

Well, here's the short of it, I have updates done constantly, so that isn't the issue....I have been told before it may have something to do with 'Codecs', but that is something I am not familiar with. So my question is this: How do you know if you are missing codecs and what do you do to tell if and what you need?

In regards to the other respondents question to me....Windows Media Player doesn't even recognize the drive that I put the dvd in to play; and the error message that I get in Windows Media Center is simply "Windows Media Center cannot detect a video dvd in the dvd-rom drive. Insert a video dvd in the drive."
I can't remember when this issue started up, like I mentioned in my original post, it used to work just fine. I have no idea what caused it to stop working.

I will try the suggestions in the post from 'Saurabh A'

I don't use vlc

With an external disc player you can play DVds - your first post.

With your internal optical drive you are not able to play the same DVDs.

In that case, your internal optical drive is faulty.

Either the DVD laser has failed/become weak or the lense occluded.

Try a CD Lense cleaner and clean it.

If it does not help, replace the drive.

How do I know if I should download the 'codecs?'
Thanks

Saurabh A said:

Hi lou62,

Windows 7 Home Premium 64 bit offers full 'DVD playback capability' and 'Windows Media Center' should be able to read it; please share if you face any 'error messages'.

You may want to refer to the following 'Microsoft Article' for more information: Playing DVDs in Windows Media Center: frequently asked questions

You may also try the following steps:
- Install 'Windows Updates'
- Update the 'Video Drivers'
- Install 'Codecs' to see if that helps: Free-Codecs.com : Download K-Lite Codec Pack 9.6.5 FULL, K-Lite Codec Pack 9.6.5 STANDARD, K-Lite Codec Pack 9.6.5 BASIC

Do reply with the results; would be glad to assist.