Why does my computer sometimes behave like this?

I use an Asus laptop computer from 2008 (yeah, it’s kinda old I guess), and although this doesn’t happen that often, it’s always quite scary when it does happen:
sometimes the computer randomly requests that I should “Install Updates” before I shut down the computer, and I choose that because I guess it’s a wise decision.
Then, when I start it back up again a while later it just shows this black screen with the message “Components: 2437 / 2437” or some other random numbers about 20% of the time.
Then it freezes like that until I shut it down and start it again (which feels very risky) and that didn’t even work on one occasion; I had to send it for repair.

Last time it happened was just a few minutes ago, and I was lucky enough to start it up just fine this time (although it did load much longer than normal, and I was very relieved when I saw the desktop).
Still, I would like to ask you what causes this, because it’s very annoying.

Invest in…Anti-virus software. The “free” ones do not work (and some of them are viruses/malware to begin with!), and the cheap ones are horrible. They do not update regularly and stop the old viruses only, not the new ones. Norton’s a good safe pick.

When have you last defragmented your harddrive? Or did a format?
Also, Redifin, there are good free antivirus programs such as Avira Antivir and BitDefender. For more advanced viruses Super Anti-Spyware (cheesy name, I know) has helped me out 100%.