After searching through several forums, it seems that the CPU keeps running continuously is a quite common problem when running Ubuntu on a computer. There are several suggestions to how to fix this issue, but none have worked on my laptop, an Acer Aspire 5739g, so far.

The best suggestion for a fix have I found, is propably this thread. However, when I tried to run pwmconfig, I got this error message:

File /var/run/ exists. This typically means that the
fancontrol deamon is running. You should stop it before running pwmconfig.
If you are certain that fancontrol is not running, then you can delete
/var/run/ manually.
I checked my system monitor and I found no process called fancontrol running, so I deleted and ran pwmconfig again. Then I got the error message:

/usr/sbin/pwmconfig: There are no pwm-capable sensor modules installed
Can anyone help me with this issue?