I have mc7 and I purchased all of the expansion packs/bundles, where are they located on my pc? I had no problem finding the studio instruments that's included with mc7.
 Once I am able to find the instruments how do I pull up the screen grid to write a song?

They should be available in Cakewalk Sound Center.

Okay thanks I will look through cakewalk sound center.
With the studio instruments I use my mouse to click on the piano at the bottom of the screen to hear a sound whether it's drums or horns. I can't play a chord or even a run with the mouse, there has to be a better way to write/play the software instruments, any experience with this or is there someone else I can contact? Thanks again!

The keyboard at the bottom of the plug-in is intended to audition the sounds. To play/record the synth use a controller. If you do not have a controller, the virtual controller in MC7 is an option.