POST: My desktop is having major issues

It is 6 years old. When we got it, we ordered it with
extra memory. We used it for our business until 2 years
ago. Just last year, we got internet service here at home
and ever since it has had issues. It will freeze up
often. It takes forever to boot up. When I try to login
to my email thru Outlook, it comes up with a box preparing
to install outlook 2003. I could get into my email only
after hitting cancel once for each message. Often when I
am online, it will give me a message saying that our
firewall is blocking access to sites. Now, it won't let
me on the internet at all. What is wrong? I am thinking
that it must have something to do with the
configurations? I can use the laptop as a wireless, but I
really need my desktop. Oh, I just added an external hard
drive. Because of all the issues it has been having, I
have wanted to back up all of my photos and docs. I have
been wondering if it would be worth it to take it into the
shop and having the hard drive wiped and then just install
only what is needed. There is a lot of "junk" on it that
I don't think is necessary, but I am too afraid of
removing it only to screw it up worse or find out later
that I really did need the software. Any thoughts?