I was asked

It isn’t just hackers that cause computer problems?

No. many problems are caused by users themselves. Many because of users lack of knowledge – or in some cases problems with there senses. sometimes problems also happen to be glitches or bugs in software.
People will blame the last person fixing their computer or friend for problems that they actually caused themselves.
Many times people download too many programs on their computer that makes it slow, or sometimes download programs that do jeopardize the security on their computer.  Also when typing passwords, people might not remember them, or mistype them and get locked out for their accounts own good.
Of course physical problems like battery issues on portables, hard drives on notebooks, or dust in desktop computers can also mess things up.
And of course you need to make sure that you don’t let other people use your computer unless you trust them well.
Another thing we have to think of is: what is a hacker?
A hacker on a technical definition simply means a programmer and does not necessarily doing illegal or unethical activities.  I have also seen it mean someone that is just exploring. The main stream media (even sometimes society) uses the term hacker broadly and usually in a negative way.
A cracker on the other hand tries to get into places that they should not.
There really are people that take advantage of others  on computers, and over the Internet. However, we need to make sure we really know how to use our computers before we blame others.