My laptop is becoming slower at times, how can I figure out if it is a hardware or a software issue?

My laptop is becoming slower at times, how can I figure out if it is a
hardware or a software issue?

Over the last month my 15 month old laptop has started showing me 100 %
CPU utilization.
I used to have ubuntu 12.10 on it. I did a clean install of Ubuntu 13.04
on it and it was fine for a while.
I run pycharm, a couple of django servers, mongodb, mysql, chrome,
firefox, a music player etc. My computer usage has not changed over the
last year. I have run 12.04 and 12.10 very comfortably before this.
My previous laptop got screwed over 3 years and I am suspecting the same
is happening here as well, but I can not see anything, like the laptop
overheating etc.
I have a thinkpad 420i with i3 processor and 8 gigs of RAM
It shows CPU utilization for about 10 minutes after startup. I have to
confess that I start all my programs with a single bash script.
After that the system usually behaves well but sometimes it starts to
annoy me again.
The question is that I want to investigate and figure out if it is
software issue or hardware issue. If it is hardware, I want to get stuff
fixed before everything goes South. How do I do it?