Not quite sure what to make of the problem. But to try and get any further will require you doing some basic checks and reporting back your findings.
In theory PowerDVD or WinDVD trial versions should have given you the required DVD playback. So there could be a number of reasons (including flaky Vista drivers) and you will need to start at the beginning making some basic checks. First are you absolutely sure your system is fitted with a DVD drive - most likely it is (most modern systems use DVD rather than CD) sorry to have to ask but trying to eliminate the possibility of only having CD device.
1. What DVD's have you been trying to play and what if any success have you had?
2. Please check in Device Manager for the exact manufacturer and model number of your DVD
In Vista to access Device Manager, go to Start start menu | Control Panel | System and Maintenance | System | Device Manager A list of hardware will display like the one shown below.
Click on the '+' next to the DVD/CD drive entries and select your listed DVD.
Are there any yellow or red exclamation marks?
What exactly does it say for this entry?
Next right click on the DVD entry and select properties from the menu. A dialogue box will open with various tabs - make a note of what information is contained under each tab and report back
3. You stated that you downloaded either PowerDVD or WinDVD. Could you explain precisely which one, how you downloaded and installed it and what result you get when you either a. Try and run a DVD or b. Click on the application to run it?
4. Similar to the above what did you do exactly with the K-Lite download?
5. What else have you tried e.g.
Cleaning the lens?
Any new drivers installed for your system?
Other?
6. Assuming the device is a DVD writer have you ever tried burning your own DVD's?
Cheers
Tony