I recently purchased my first personal linux machine. Twice in the past week I've had my machine freeze (mouse stuck, unresponsive to keystrokes, etc.) while doing seemingly non-intensive things (the last time I only had Firefox and the Ubuntu software center up and was scrolling through the software center when it happened). I've seen two suggestions in forums for solving the problem and neither has worked - CTRL + ALT + BACKSPACE, and ALT + SysRq then REISUB. Has anyone else been experiencing this or know of any known bugs/solutions? Any help is appreciated. Thanks!

It might help if you posted some info on your hardware. Does this happen with other operating systems on the machine or is Ubuntu the only OS?

Ubuntu is the only OS. Since I don't know much about computers or about what hardware may have something to do with it, I just copied out all my specs below. It's a System76. Thanks for your help

Ubuntu 12.04 LTS 64 bit
14.1" 720p High Definition LED Backlit Display ( 1366 x 768 )
Intel High Definition Graphics
3rd Generation Intel Core i7-3610QM Processor ( 2.30GHz 6MB L3 Cache - 4 Cores plus Hyperthreading )
8 GB Dual Channel DDR3 SDRAM at 1600MHz - 2 X 4GB
240 GB Intel 520 Series SATA III 6 Gb/s Solid State Disk Drive
8X DVD±R/RW/4X +DL Super-Multi Drive
Intel Centrino Advanced-N 6235 - 802.11A/B/G/N Wireless LAN + Bluetooth Combo Module

It might be a good idea to run all the updates available in the packages manager.
I am assuming you have the sudo password for the computer then open up a terminal and type
then type your password and let it do its thing
after is done running all the updates type
type your password again if asked and let it do its thing, once is done running all the upgrades type
After rebooting do all the things that used to lock the computer to see if it is cured.
Give it couple of days and report back how you did.

By the way terminal is the icon that looks like a black screen with a >_ showing. Look it up on your launcher dock.

good luck to you!

Defiantly do what Tron says.
I personally don't like Ubuntu because i find it buggy and found similar issues as you described when i used it. I haven't used it in a long time, but i think Ubuntu uses Compiz as the window manager by default? if this is the case, you may want to try switching it over to metacity or something and see if that cures the problems (if you can do that in Unity), because i've found compiz to bug up even in the notoriously stable Debian and Slackware. If that doesn't work, switch distros/os for a little and see if you suffer the same problems, and if you do you may have a hardware issue.

I wouldn't blame the hardware just yet.
I tried Precise (12.04) a couple of months back - and gave up in disgust. Seems the freezing is not uncommon - see my post here.

Just to be clear, i am not blaming the hardware straight away. I think the op should try switching compiz over to a different window manager (if compiz is used by default). If that doesn't help i suggest trying a different distro; and if the problems still persist in all those situations, only then do i think the hardware should be checked.

Thanks all for your replies. Based on syg00's thread, it looks like a refresh is coming out this month so I'll probably cross my fingers, continue to update, and hope that the coming updates resolve some of these issues. If not, I'll return to this and reconsider my options. Thanks again, guys!

Odd advice here, especially considering it's a new computer. I've never had a Linux system freeze up on me, ever. I'd run checks on your memory, a bad memory stick can cause exactly this problem. I'd also turn off compiz and desktop effects and see if that makes any difference at all.

why don't you try my suggestion. its easy and you can try it right away.
enter this command
that will flip the window manager over from compiz to metacity. you will need to launch that every session. see if the freezes persist while using that window manager.