Need help, please: EMC2 is will not open.

That is a fairly old version of LinuxCNC, but that isn't a problem if it does what you want. And it almost certainly will.
There have been some new features introduced between 2.4 and 2.6.3 (the current release) but I would suggest getting familiar with your machine and the system before bothering to upgrade.

There are configuration changes that need to be made upgrading from 2.4 to 2.6 without which the upgrade will stop your machine working again, which is why I am suggesting deferring the upgrade until you know that you need it.

You can view the changelogs here to see if you have any "must have" upgrades in later versions.
wiki.linuxcnc.org/cgi-bin/wiki.pl?Released