Finally got round to calling Dell back regarding the microphone not working after the laptop display was replaced. Got through to the right dept quickly, let him access remotely so he could check everything and uninstall/reinstall as needed. He was efficient, told me what was happening , what he was expecting. The upshot is that a new display is needed and someone will be round to the house tomorrow to fix this. Like last time I spoke with them over the phone I could not find fault. Perfect Support from Dell.