Restart the computer. If you cannot get your computer to restart the normal way - press and hold the power button for a good minute, and it will eventually switch off.
Restore the computer if it was working well the day before and is giving trouble today - select a restore point - all the data be retained.
Having trouble opening email attachments such as pdf documents, check that you have the correct software installed to open the attachment. Google the the question in such a way "program to open pdf files". Then check you have the suggested program installed, eg Adobe reader.
Pop up ads appearing on your machine can be safely removed using Malwarebytes.
Check your hard drive has plenty of free space. If the hard drive in Computer window is red - then it is too full and more space needs to be created in order for your machine to run effeciently. This can be done by deleting unwanted data files and doing a disk clean up.