Old browsers - how to update them?

I am ever so new to Ubuntu that I didn't dare look to see if that was already answered, in case it was too full of hard-to-understand guidelines, so I appreciate your time and effort in trying to help me!
I have several problems with my Linux Ubuntu which I had installed by someone several years ago, whom I caot now ask advice to.

First of all, my 2 browsers, Google Chrome and Firefox both are outdated, crash at random places and won't let me view videos (why? Since it worked before, why should it stop working?) .

Secondly, I have a flaw with the whole Ubuntu system, which after a few seconds of starting up, says "problem system detected" . And there is a "no entry" symbol on the middle top of the screen with the other computery icons. When I click on that, it gives me a write-up which I don't understand.
Now, I have heard by searching online that I needed to re-instal Ubuntu so I bought a CD from someone on Ebay who was very reluctant to give me any help after receiving the cd, as to how to install it; I understood I could either use the program to "look into" my computer (as some of my folders won't open, they are blocked by that problem) or re-install it entirely, which I am definitely NOT confident in doing. I am not confident in anything really, regarding computer things - as I am not used to Linux and have had no tuition on how to use it and none of my friends use it so I can't ask anyone.

I have lived with the "Problem SYstem detected" difficulty for years. I just can't access my files, that is all. But the old browsers which won't let me watch videos, is another matter!
Now, I did download earlier 2 new Firefox updates (or the whole program, I don't know) but nothing happened. I tried to open those folders, found a title that said "Run Firefox" in one of them (not the other download, oddly, though I thought I downloaded 2 of the same) and clicked on it, and nothing happened except seeing a list of what looks like alien language.

I feel totally frustratingly useless at understanding what to do, or attempting to do it. Could someone help me just enough to at least get one of those browsers properly working please?
If not, well, not to worry. I will live with it till the computer stops working..But I did like Linux. Well, except I can't use most of it, but what little bit I could use was rather nice.

Thanks in advance for your patience and sorry if this irritates some of you as you must get a lot of that, people who don't know what they are doing, asking "stupid" questions...
Alexandra