"Phone restarting or freezes whenever it wants. Any suggestions?"に関する回答Well, try restoring with Windows Device Restore Utility. If that doesn't help, check out this guide, open your device and try to figure out what's wrong: http://www.smartphonefrance.info/Techniq...
"How to change the mic?"に関する回答The standard answer you will find is that you will have to replace the motherboard. Let the Nokia people do it, they know what they are doing :)