I have a multimeter but don't know how to use it and if I should check the voltages can you guide me on how to check it and what to look for?

To start with I would have a good read through this.  http://www.pinrepair.com/sys1/index.htm#power

Basically you will need to remove the connectors from the power supply and check the voltages as described in the guide.  If you aren't to keen on doing stuff like this, I would recommend sending the board/s to ken/Skybeaux and they will come back in tip top working condition.