Hotmail keeps jumping to ads - soooooo annoying

[lalalonglegs]

I have a hotmail email account - it's my only email account and I use it a lot as I am self-employed. Over the past couple of weeks it has been continually jumping to adverts every time I try to open an email/my inbox etc. There seems to be no way to get rid of these ads and they do not disappear after a few seconds which means that I am continually having to press the "Go Back" icon and try again, sometimes several times. Why is this happening and what can I do to stop it? (I use a very old Mac which seems incapable of uploading any new programs.)