I talk to my sister every week in Ireland and suddenly her cam won't connect to my laptop.We get sound but no picture. Could I have blocked web cam by mistake? if so how do I rectify it?..
Are you sure not her cam, can she see via her cam. Might not be you blocked her. Might be drivers on her pc she needs to check in hardware manager, via system in control panel, see if the cam is showing, with a query next to it.
IF not and you need to post again, Operating systems used etc will help
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Try fixfault.com to fix webcams.