Not sure why you want to erase hard drive. Without external cd/dvd drive, no chance to reinstall Win 7 and programs. Also appears you do not have the Win7 installation CD. You will also need to make sure you have note of your Win 7 serial number and a backup of your documents, emails etc.
I suggest you restore the notebook to factory settings. You will of course lose all your documents unless you have them backed up. You will need a USB memory stick for that or in the cloud with Google,MS outlook Drop box to name a few.