Steam window doesn't respond

[Mozi111]

Recently I booted up my old computer and installed Ubuntu on it. I am not a Linux user so I don't know much about installing drivers and things like that, but I think I installed all the necessary. I've also installed Steam from Software Center. It's all normal when it starts up (looks for updates, gives me the log-in window), but after I log in and the Store and Friends page come up the windows stop working. I can't move them or click any button in them. They do however highlight (over other windows) if I click on one and if I order Steam to go to Community (by right-clicking on the symbol on the top of the screen and pressing Community) the windows loads it up too.
As I said I am not sure if this is a problem with Steam, my drivers or just that my computer is too old to handle it, but I wanted to ask if there are ways to try and fix it (I used search a little, but it only found different problems).
Thank you for your help.

[Mozi111]

And if I start Steam in Terminal, this warning shows up while loading textures:
(steam:6533): Gtk-WARNING **: Failed to load type module: (null)

I also tried steam - -reset and clearing cache, but it didn't work.

[Kranky K. Krackpot]

apt-get install appmenu-gtk?
Can you post full output on pastebin.com and give us link to it?

[Mozi111]

I don't know what exactly happened, because I've restarted my computer several times yesterday, but Steam started working today. Thank you for your help anyway.