please read carefully.
you have an intel atom z36xx processor, onboard graphics.
i couldn't find any info about that, but i'm under the impression that atom processors are somewhat old.
you have to do some research if linux graphics (the i915 module) is known to have problems with this particualr chip.
generally speaking, you shouldn't expect the world from onboard graphics and i think it's time you told us what sort of "stress" you're talking about.
oh, you said it already:
downloading or installing should not stress the graphics card at all.
it's hard drive input/output and networking activity.
how do you connect to the internet?
if it's wlan, i think you should use 'b43' module instead of the currently running 'wl'.
(it will also need additional firmware. please search your distros help pages on how to do all that)
broadcom chips + wrong drivers have been known to freeze linux systems.
there's probably some way to look at some logfiles, and go at the problem scientifically, but it's difficult if your system freezes completely and only a hard reboot works...
however, next time you get a freeze, try this:
press Ctrl+Alt+F2 on your keyboard.
if that brings you to a text console with a login prompt, log in normally and type the following commands:
dmesg|tail -n 50
sudo cat /var/log/Xorg.0.log
sudo cat /var/log/messages
sudo cat /var/log/faillog
sudo cat /var/log/syslog
and copy-paste the output here.
you probably might want to redirect the output to a file by appending " > filename" after each command (see here
on what that does and how to use it).
this will produce a crapload of output, so please don't just dump it here, but make sure which output belongs to which command and paste them in seperate codeblocks.
you can do the same from a running graphical desktop and in any case also have a look yourself
, maybe you can find something. the relevant entries are usually marked "error", "E", "fail" or some such.