Are you able to load windows?
I am assuming you are running windows 8. If you are, you can open up cmos through windows.
Here's how
1. Bring up the charms bar and open settings
2. Open Change PC Settings
3. Open General and scroll down until you see Advanced Startup
4. Click Restart Now and let it do its magic.
At the Choose an option screen, select Troubleshoot
Click Advanced Options and then UEFI Firmware Settings, which will then restart into cmos.
I have an Aspire E1-571G and it works that way on mine, although yours may be a bit different.