Hi guys, I'm new in MC7 but I had a non-original copy of Sonar X2 before. Anyway, I don't have the Cakewalk Bass, Drums, Electric Piano and Strings  vst's, but it supposed that comes with mc7. 
I have 6GB of Ram, so I have Windows 7 64-bit, and already tried installing the 32-bit & 64-bit version of mc7.
I'll really appreciate you help, Thanks.

I don't understand what you mean by a "non-original copy of Sonar X2"?
 
forgive me if this is too basic, but you haven't given us much to go on, so I don't know what you've done and what you haven't.  where are you looking for the Cakewalk Bass, Drums, EP and Strings?  are you trying to insert them from the browser, or from a different path?  this tutorial should help you insert them.
 
https://www.cakewalk.com/Documentation?product=Music%20Creator%207&language=3&help=Tutorial4.2.html
 
if you've already tried that, but can't find any of the instruments that way, then follow these instructions:
 
https://www.cakewalk.com/Support/Knowledge-Base/2007012922/Cant-Find-Cakewalk-Sound-Center-or-Other-VST-Plug-ins
 

Hi, what I mean with a "non original copy of Sonar X2" is that I'd downloaded it without paying but just to learn about how it works, and then choose this DAW, or still seeking in other place. I just said it to explain that I have some knowledge about Sonar.
I'll start from the beginning. When I downloaded MC7 (purchasing it before, of course) I just install it and open. Then create a new blank project and tried to use the Cakewalk's VSTs. But when I click on Insert Synth on the Synth Rack, the only VST that I could see was the Cakewalk TTS-1 and not the others (Drums, EP, Strings, Bass).
So, I tried to create a new project with the Songwriter Collection template (this one includes already the drums vst and some more) but I get an error that says that some plug-ins are missing, and then it mentions which vsts are missing.
And I couldn't even install the Kawai EX PRO piano library that I bought recently.
 
PD: If there's any mistake of any type, sry, I'm from Argentina and don't speak English so good yet :P

Did you install all of MC7? Click the arrow to the left of the Music Creator 7 line to expand it. The dots are green if installed, red if not installed.

Hi, no i didn't. Actually I opted for download just the program installer, not the command center download. Could be there the error?

The program installer does not contain the other installers listed below it. The studio instruments suite contains the SI-Bass, SI-Drums, SI-Piano and SI-Strings.

Ahhh, Ok, I get it now. Thanks dude, I'll try downloading and installing all from command center tonight, tomorrow I'll comment what happend. Really ty

If you are not using the command center, all of the installers are in your account too.

Ah, so technically I can download it separately

They are all separate downloads whether using the command center or not. The command center is there for your convenience. It is your choice to use it or not.