From what I can tell from your LED strip manufacturer's website, your 5-meter (300 LEDs, 100 3-LED segments) 5050 LED strip consumes 40 Watts...or 8 Watts per meter.
Your 12V power adapter can supply 750 mA or 0.75 Amps. Watts = Volts x Amps, so that's "only" 9 Watts.
So your adapter can power about 1 meter of your 5 meter strip. That's about 60 LEDs or 20 3-LED segments.
If you look at the manufacturer website they recommend a 60 Watt power supply adapter.