Missing D Drive

I have lost my D Drive on my Lenovo Laptop. I am using Windows 7. It only shows my C drive and now i am unable to run my DVD. I recently changed my start up programmes because the laptop was hanging on the Lenovo screen and stopped Dropbox from starting up at switch on.

I ran a restore to a previous date yesterday but this has made no difference.

Any suggestions would be very welcome.

start
right click computer
manage
device manager
click once at the top of the middle listing on the name above computer
click top menu action
click scan for hardware changes

Thanks I will give this a shot.

Thanks I tried the above but when I click scan for hardware changes it just flashes up then nothing happens.

Wonder of wonders, I inserted a dvd into the D Drive and hey presto it worked!! It is now showing on my laptop that I have another drive.
Don't know how this has happened but am delighted.