"You need to restart your computer"

Wow, I've only had that happen once or twice in the last 8 years! It's not normal at all. That's when the computer freezes really really bad I just restarted and had no problem afterwards, but I don't know if there's anything else you can do

 

Sounds like a Kernel Panic.

Nothing to worry about if it is a one time occurrence, though make sure you have current backup of all your most important data (like photos, work, etc). Kernel Panics can be caused both by shady software (the official But Torrent client played havoc with my old machine a couple of years ago) or failing or poorly fastened hardware (bad RAM, loose wiring or airport antenna or similar).

If it becomes a regular event (and you're not running any weird software like bit torrent or system hacks) it's time to take it back to the store (or, if it's out of warranty, to a service provider), and get the hardware checked out.

 

Since you just had this problem where it looked like the desktop folder wasn't behaving properly...and now this, I'm gonna recommend you rebuild permissions following the steps in this guide.

Also...post what you were doing at the time of the kernel panic in case someone might be able to see a possible connection between the two.

 

had my first one earlier on, I was right in the middle of photoshop too which didn't make me too happy, luckily I had saved my work not long before

 

I just had one the other day also. I didn't realize what it was, it didn't faze me in the least. I guess I just got used to it while using windows. I just restarted it and haven't had any more problems. Next time I will keep an eye on it.