Hardware Troubles

So lately I've been using my old but wonderful Lenovo Thinkcentre 8113D1U to import blocks of data onto the internet. This involves leaving my computer on overnight. This has lead to an increase in problems that I have had both on Trisquel and when I used Ubuntu.
Either my computer is running, but no signal goes to my monitor (this is more frequent in hot weather), or I get a message saying that "Ubuntu" is running in low graphics mode, am promoted to restart X, then told to "wait a minute while the display restarts." Since nothing happens, I click the okay button below the full loading bar, the system switches to a series of text processes similar to what I get on boot. It freezes on a check of battery state (I'm running a desktop) and I have to restart.
In either case attempts to access my computer though SSH fail, the first error occurs only when the computer is idle, I have discovered that launching the game Solarwolf will cause the second. My brother's server is a near identical computer that runs Ubuntu which does not have these problems.
I tried replacing the thermal paste on the processor and cleaning everything, but that did not work. Aside from getting a completely new computer is there anything I can do?