While I have not done voice over recording before you asked the question, I did learn some MUST dos to make a voiceover recording in PD8.
1. You must have a video in the Main video track.
2. (May be system dependent) you must have a microphone plugged into the mic jack, and you must configure that mic input in your computer's sound device. (My computer has an auto detect, and pops up the dialog).
3. You must set up the device button in Voiceover room, for my system, it was Realtek HD audio input. Audio input, Mic volume. PD does not seem to remember the device button setting.
4. You have to select a profile for the audio format. Preselects are available, I choose CD quality. Radio quality may be is a good choice also. (A filename in the save as is a good idea, PD does have a default name)
4a. The button will now be red.
5. You can pretest the mic volume and make adjustments.
6. click the red record button to start playing the video and recording your voice.
7. The red button turns black and is the stop button, press Stop to end recording.
The above worked for my test.
Carl312: Windows 10 64-bit 8 GB RAM,AMD Phenom II X4 965 3.4 GHz,ATI Radeon HD 5770 1GB,240GB SSD,two 1TB HDs.