Unfortunately this is normally something you need to get while the computer is working. You have to have a valid Product key. If you cannot boot to the OS now and install software to extract the information from the registry, and it is not printed on a sticker on your machine or on W7 DVDs, then you either have to buy replacement DVDs from emachines or if the computer has a SLIC table in the BIOS you may be able to extract the information.
Laptops and most newer computers are pre-activated at the factory. To do this, the License Key is stored in the BIOS in a SLIC (Software LICensing) Table. If you can run the OEMtool and extract your W7 license key from the BIOS then you can use that product key to activate a new W7 installation on that machine.
I have never used this myself and to get it you have to join their forums but it may be worth it to you. On the site
MyDigitalLife they have a tool (the OEMDUMP Utility) that is supposed to extract SLIC information from the BIOS.
NOTE: Please be careful on that site and be sure to scan any downloads for viruses (you should be doing this to downloads from any site really). They are extremely smart but I suspect many of them are also hackers.
