Under event viewer you need to look at System and Application sections. You will find any error events highlighted in yellow or red. Someone will tell you the meaning of any red 'error' events if it is not pretty clear what they mean at first sight.
I suspect your problem is just that you do not have correct windows 7 drivers for your DVD drive. Check the website of your DVD driver manufacturer for drivers specifically for Windows 7, your motherboard manufacturer for general disc drive drivers, and if appropriate the PC seller for all drivers.
There remains the possibility that the DVD drive is now faulty - they are optical and mechanical and pretty cheaply thrown together. If it is important to you, simple replacement is an option.