Replacing RAM is not hard. But let us first see if it really is defective!
There is a package for that: "memtest86+". Install it, e.g., with the
"Synaptic Package Manager" or with the following command (to be executed in a
terminal):
$ sudo apt-get install memtest86+
Memtest86+ does not run inside GNU/Linux. It is to be executed from the
bootloader. Do you have, almost right after switching on your computer, a
two-entry menu with "Trisquel" and "Advanced options"? If so, memtest86+ must
be inside "Advanced options". The problem is, GRUB will ask for a user name
and a password. The user name is "grub" and the password is a number that was
randomly generated when you installed Trisquel. You can read it at the end of
what this commands (to be executed in a terminal) outputs:
$ sudo cat /etc/grub.d/01_PASSWORD
If you manage to execute memtest86+ (otherwise please explain in details what
you did and what is the problem you face), let it run for hours (e.g., for
one night). If the screen turns red: the RAM is defective. Otherwise, it is
OK.
