Why can I not see my second hard drive?

Brought homw the new HTPC

It has a SSD as the main drive and a 2 TB hd as the second.

When I installed Windows it gave me the option of which of those two drives I wanted to install windows on.

Over the next few days I ran the disk provided by my mobo to get things going.

Installed XMBC and Powerdvd watched a BR and added files from an external to the XMBC library.

Now today I went and plugged in another external (as it was old and I had forgotten what was on it). I used Windows explorer to see it by clicking on computer. That's when I noticed that I could see the
SSD, both externals, the BR drive but not the internal 2 TB drive.

Also, there are two other drives that you can see.... each one is associated with one of the two externals and has little to no memory.... they always appear and I've largely ignored them over the year.

Looking at the Silverstone case I flicked a switch that opens a swinging door and I could see the 2 TB drive inside and the case had a blue light (which I assume indicates that hte drive in that slot is recieving power or active.

How do I trouble shoot this?

Any thoughts would be appreciated.

Okay went to programs, accessories, sytem tools, system information, components, storage, disks

here it gives me description of two fixed hard drives the ADATA which is my ssd and WDC WD20EARX-00PASB0 which i assume is my WD 2 TB green drive as it's partition size of 1.8TB makes sense.

This was the only place I was able to see evidence of the second drive

Is there something to do with the motherboard or when you set up the computer because I broght it home, installed windows, ran the mobo provided disk but maybe I didn't do something to activate the drive?

Looking at the two drives on the screen for the ssd it describes the partition
disk 0 partition 0
disk 0 partition 1

but for the WD HD
it just says
partitions 0

Mind you I have not even set up partitions of any kind yet

1) Thank you for the responses!

2) I will provide a screen shot when I get home from work tonight

3) Thanks for the directions to get to disk management..... I typed it into search line when you click on the windows icon but came up empty handed. Maybe it was an older version of windows where disk management was found in the program section or just hazy memory. Anyways, Win 7 64 bit does not.

I typed windows disk management..... will have to try without the word windows tongiht. LOL

Googled WDC WD20EARX-00PASB0 was happy to see that it was the code for the WD green drive.

Can't wait to get home to make a screen shot and try out disk management.... if it sees it will I have to format or partition it?

Part of me thinks that's possible as the people who assembeld the PC would not have been able to do that prior to me installing windows. Is that line of thinking correct?

Googled WDC WD20EARX-00PASB0 was happy to see that it was the code for the WD green drive.

Can't wait to get home to make a screen shot and try out disk management.... if it sees it will I have to format or partition it?

Part of me thinks that's possible as the people who assembeld the PC would not have been able to do that prior to me installing windows. Is that line of thinking correct?

Okay a 1000 Thank Yous!

Yes I used Disk Management...... my probelm was when I searched I was literally looking for something called that and the search returned the phrase given by a helpful poster above.

I assigned the drive a letter and then formatted it.

I had done this before but in my defense the last two times I did this was for

1) an IDE drive

2) a SATA based 750 gb external that I made with an enclosure because it was cheaper than buying a premade say WD My Book at the time