You should have run Windows 7 Upgrade Advisor
from Vista which would have told you exactly how it will run and why.
Before you do anything further report back the PC's model number from the eMachines sticker on the back or side. We'll then tell you whether and how you can install Windows 7 on it or go back to Vista.
Because you probably didn't boot the installer to correctly install Windows 7 deleting all partitions, you may have a windows.old folder that can be rolled back to Vista, or the Recovery partition may even still boot and run to reinstall Vista.
But Windows 7 may in fact run on that PC, as it does fine on a 8 year old T5234 I have. If so we'll help you get a perfect install. Look over these same steps for Clean Reinstall - Factory OEM Windows 7.
Waiting for the model number...