Windows Media Player won't launch on Vista - how to repair or reinstall it?

Windows Media Player won't launch on Vista - how to repair or reinstall it?

My friend asked me to look at her Acer Aspire laptop with Vista Home Premium as it is no longer playing DVDs. I found that Windows Media Player would not launch. I found this thread, which contained a number of suggestions, none of which solved the problem. Here is what I tried: