Did you partition and format the drive after the install? It will not show in Explorer until you do.

If you have a CD of software that came with the drive - use it to partition and format.

If you got a bare drive then:
type diskmgmt.msc in your run command
You should see the in the graphical display on the right of the screen.
Right click the drive and a drop down menu should give you a choice to partition:
you should partition it as one big partition the full size of the drive.
Then go back and right click again and select format

after that (you might need to restart windows) you should see the drive in Explorer (My Computer)

Good Luck

I use gigabit mobo with one slot for IDE and 4 for SATA devices. I have IDE hdd as master with OS in it, share with dvd rom as slave. A week ago i bought a new hdd SATA to expand my free memory space. Thats mean i want to use it as secondary hdd. When i first install it (SATA 1), it seems conflict with my dvd rom. So my friends suggest that i unplug the dvd rom first. Thats it, after format the hdd, i can use it. But the problem comes when i want to install back my dvd rom. My computer don detect it at all, even in device manager. So i pull out the jumper at the dvd rom (my IDE hdd still have the jumper as master), where i put it before at slave. I dont use it at all. Then i install it, and my computer detect it. I can use it now, but my computer start up loading window be very slow. I feel not comfortable with that.
At last i change the connection of my new hdd SATA at the sata 03 port, and i put back the jumper at dvd rom as slave. For my computer this is the solution, make it smooth like usual. And at the Cmos it look like this,
IDE 0 master : my old hdd
IDE 0 slave : my DVD rom
IDE 1 master : none
IDE 1 slave : my new SATA hdd.

Hope this may help somebody.