Need Help!- Lasercut 5.3 configuration on laser machine

[Computer Cad]

Hello friends, this is the first time I write on this forum and this is the first experience for me to use a laser machine, too.
I bought a chinese laser machine SF1290 100W. Together there is a software called LASERCUT 5.3. I bought it one week ago and this week has been a calvary for me!!! If I set for example speed = 1 and Power = 90, I can cut trought 1cm of thikness of acrylic. If after the cut, I set speed = 1 and power = 40 I can cut it, too. If in the other moment I try to cut it again with the same parameters, the machine doesn't cut it more... neither 40 then 90 of power.
Can anyone help me to set well software? It is important the LASER FREQUENCY value? (it is setted of default to 25.000).
Another example is that if I cut with power of 40 - 90 and speed = 1, it can cut it (acrylic 1cm). If I change speed value, for example to 2, the machine can't cut trought the acrylic, neither if I set power to 100.
Thanks to all good people that will help me!!!