I have cakewalk files dating all the way back to 1999 (wrk files). I am able to open them in Cakewalk Sonar latest version on Windows 7, and I see the tracks. When I play, I don't hear anything. My laptop volume is set at max. I see the 2 green bars bouncing up and down next to the track, indicating there is data, but no volume is heard. What do I need to set just to hear the old track? Thanks.

Sonar what ? Platinum, Artist or Pro ? And what kind of Soundcard are you using ?
You need to establish a soundcard device.
Go to preferences, Audio devices and make sure your soundcard is selected.
Driver mode would be ASIO if possible but if you are using your onboard audio try WASAPI or more than likely you'll have to resort to MME.

Make sure your mains bus output is set to something correct. It likely isn't.

Thanks. I'm using Sonar Platinum Demo version. I tried going to Preferences and setting ASIO and WASAPI, and it still doesn't work, no sound. I'm only using a Windows Asus laptop, no audio gear hooked up to it. Sorry for the beginner question. 

Download asio4all which is an asio wrapper for run of the mill onboard sound cards in laptops and desktops. Not for serious work but should allow you to then go asio mode.

Thanks. I installed asio4all, but no luck either. I select ASIO mode under Preferences and Devices. Do I need to set volume for a particular track? I'm just running the default install of the Sonar Platinum, then opening my old wrk file, and then setting devices, and then clicking Play button. 

To widen the picture:
If you start a new project and insert a soft synth or connect a  mic or guitar, is it mute as well?
Are the wrk-files audio or MIDI or both? What are the track/project outputs set to?
Record & playback timing master?

I suspect that the master bus out might be set to "None".

If your just playing back tracks, select your sound source in Audio devices.
Make sure in devices it is checked off (for output).
Then make sure your master bus is set to hardware bus and your hardware bus is set to your soundcard.

What's in the tracks? Recorded audio or MIDI?. If MIDI, you were probably using your PC's soundcard synth in 1999, and need to change the Output assignment of the tracks to your current soundcard as a MIDI device. If it's not available as an output, you'll need to confirm that it's listed under MIDI Devices in Preferences, and is enabled (checked).
 
If you want to update the project to use soft synths (advisable), try inserting Cakewalk TTS-1 (a multi-timbral General MIDI software synth that emulates a soundcard), checking the option to have SONAR create the first audio output track, and then assign the Output of all MIDI tracks to TTS-1.