Creating a slider on front page – images won't upload

Hi
I’m new to WP and am trying to create my first website. I have created a static front page but have decided to create a Slider too, then I can decide which one to use.

When I click onto ‘Add image’, and try and upload the image from my laptop, it shows a http Error message and won’t add it to my gallery. The pictures I am trying to add to the slide are from the internet but have been saved onto my own laptop as a .png file.

I have added pictures on other pages on my site and these uploaded fine – all of a sudden it won’t work.

Does anybody have any idea why I can’t upload them???

I don’t think WP is as easy to use as we are led to believe when purchasing it……

Thank you.