Thank you for the added details. A few things about your computer:
1. The Lenovo IdeaPad 100 series is a very basic computer with a very affordable price tag. In fact, it's so basic and so "affordable" that it's not really designed to last for more than a year or so. Depending on the cost-of-living index of your country, this may sound somewhat arrogant, but this is how Lenovo has designed this laptop series.
2. I know I said 'more than 5 years old' earlier, but with very basic computers I regret to say that it is not uncommon for them to malfunction even after a little more than 1 year. This is most likely what happened with the HDMI port in your computer. Whether it's been knocked loose or some electrical connection no longer works...