Q: my macbook pro (mid 2009, OS X 10.9.5) has countless issues

It started when I noticed frequent crashing of FCPX, (many different kinds of crashing, i.e. the "The application detected an error that prevents changes from being saved. To avoid losing your work, quit Final Cut Pro." message, the "final cut has stopped working unexpectedly" message, and frequent kernel panics"

I recently some corrupt data and hard to start from scratch (I didn't have any time machine backups at the time), but I managed to get it kind of up and running again, but still with the same issues as before.

I did some research and found that occasionally frequent kernel panics are the result of out-of-date software, so I decided to go ahead and try upgrading to Yosemite. Here I encountered even more issues. At every attempt of downloading Yosemite, I would receive some kind of error message (that the download was corrupt, that I should restart and try again, most notably "An error occurred while extracting files from the package 'Essentials.pkg'."

I went to another thread regarding troubleshooting problems related to difficulties installing Yosemite, and found that it could potentially be a hardware problem and have nothing to do with Yosemite. In order to check for this, you'd have to use Apple Hardware Test. However, I am unable to run AHT because I purchased this computer off of craigslist, and so I don't have the cd's that some with it.

I seem to have reached a dead end in every sense.

Any suggestions (besides "purchase a new computer"?)