> Right now, I would squeeze the life out of the person who made this game if given the opportunity.
Yikes!
Let's start at the beginning.
1. Which exact Galacticraft and Forge versions are you using, did you get them from the official sites, and are you sure the downloads completed?
2. Do you have Minecraft + Forge working 100% OK without Galacticraft in your mods folder - or do you have other issues?
3. Please read this from beginning to end. I wrote this personally, and it's designed for dads, so if something is wrong or not clear in here I am interested to fix it.
https://wiki.micdoodle8.com/wiki/Tutorials/Galacticraft_Installation_Guide (I'd hope this should have come up in a Google search for how to install Galacticraft.)
4. Is there a specific reason why you
have to use Minecraft 1.7.2? Minecraft 1.7.10 is more stable, faster and has less graphical glitches. The only people who have to use Minecraft 1.7.2 are normally people on older laptops, like 5+ years old (like mine).
5.
commons-codec-1.9.jar that you mentioned is a standardised library file for Java. Galacticraft tells Forge it needs this file. Forge should then
automatically download this, the first time you play Galacticraft, and should automatically place it in your
mods/1.7.2 folder. You can also download the file manually from
http://central.maven.org/maven2/commons-codec/commons-codec/1.9/ (it's number 15 from the top, with the number 263965 next to it). Though really a manual download shouldn't be necessary. I've never heard of the automatic system not working, before - though you do need to be
connected to the internet obviously, the first time you play Galacticraft. It's a quick download, the whole process happens transparently for most players so it's not even mentioned on the Installation Guide. (I'm actually kind of interested to know why it didn't work for you?)
I have sent you my personal email and Skype via private message here, so I can help you directly with this if the above doesn't get you going.