Email attachments won't stay open


New Email
I have been using yahoo mail as my email preference for years. Suddenly, my email attachments such as my online electricity account, will not stay open. I have tried opening them from the "downloads" file, and from my email itself, but the same thing happens. It will stay open for 5 seconds, and then disappear, taking me back to the body of the email I was in. The whole page disappears. I am not that techno experienced, but would love somebody to tell me why this is happening, and how to stop it happening.
I use Google Chrome as my browser currently. Also at the moment, I am having trouble opening and using acrobat reader, and viewing pdf files. I am unsure whether this is something connected to my attachments.
I would appreciate any assistance anyone can give me please. :confused::(