Reboot and select proper boot device or insert boot media in selected

Did anything happen to your computer recently?

This seems like a problem with Master Book Record and that the hard drive is no longer configured as bootable.

Nope its not that, in your bios you have set the network adapter to boot from Pxe. it can be a rom chip on a network card, this type of system is used for what we call terminals, where when it comes to booting and loading an OS it is stored on a master server.

In anycase your boot order is set wrong with in your bios, and more than likely you will find in the boot order that the network card is listed at 1. You need to change it so that your HDD is set to one. The test by the way had to do with checking an network cable that is plugged into the device. so if there is not one connected,then you will see the error like you are seeing.
Also there will be an option to boot from ethernet/ Nic rom turn it off in the bios also.

I just noticed that when I entered the BIOS. Under the main tab it says "None" for "Fixed HDD"! I don't know much about computers but doesn't mean that the HDD is perhaps dead or disconnected?

Check you cable.... the drive may have died.

Sorry I am new at this. What cable? This is a laptop.
Thanks.

Unplug the laptop... remove the battery... open the trap door on the bottom of the laptop remove the HDD and reinstall it... cross your fingers and plug it all back up and see if it works... it may be time for a new hard drive? do you have system restore disks?

It's not as easy as you think. It's Dell Inspiron N5010. I looked up on You Tube. It's a hell to get to the HDD. This Dell sucks.  
Thanks anyway.