Command prompt isn't a very useful tool for DoSing. LOIC (Low Orbit Ion Cannon) is common among most script-kiddes and is an overall better program. You shouldn't be worried about being attacked if you don't stir up trouble online. You should be more worried about people getting your address and sending pizzas to your house.
If you must protect yourself, in the event of an attack then preventing DoS or DDoS attacks can be fairly simple.
Step 1: Block their IP address.
This is assuming that this is a DoS attack (coming from 1 IP address.). Use tools like Wireshark to see where this attack is coming from. Then use online tutorials on how to block IP addresses on your firewall. Block the attacker on any P2P (peer to peer) applications (like Skype) so they cannot find your IP address through them. Also, find out how to stop Skype resolvers from getting your IP. (VPNs are useful too!)
Step 2: Change your IP address
It's called a 'release and renew'. You can figure out how to do through Google searching. But unplugging your modem and leaving it unplugged for a long period of time (8 - 24 hours) should work.
Last resort
If nothing above has helped then contact your ISP and ask for help.