I keep getting killed, even though I shoot

Hint 1 of 7:

Did you buy any ammo for the gun ?

Hint 2 of 7:

Did you buy ammo for the gun you're firing with ?

Hint 3 of 7:

Did you buy a force field shield to help protect you (page 48, top).

Hint 4 of 7:

Get a high powered one, at the Shield shop.

Hint 5 of 7:

Be sure to have cursor on attacker while you fire.

Hint 6 of 7:

Shoot faster. And try changing your cardiogram to ACCELERATION.