737 NGX giving me DES PATH UNACHIEVABLE !

hello everyone!

So I'm a bit new to the FMC and mediocre at FSX, learned most of the cld/drk operations yesterday, and departed KLAX 25R last night headed to KLAS 25L. I placed the correct waypoints to KLAS from KLAX including leaving the airport through proper airways and landing the aircraft at the proper runway using the waypoints on approach.

I simply did this by opening my FMC and entering my Origin and Dest as KLAX and KLAS, I then clicked next page to get the get the VIA route page. Here I entered every single waypoint as follow and they were all DIRECT on the FMC. 

ADORE-SHAEF-PEVEE-HOLTZ-OSHNN-SLI(115 degrees)-SEBBY-DAG

CLARR-SKEBR-KEPEC-IPUMY-NIPZO-SUNST-KIMME-CHIPZ-POKRR-PRINO

with landing to waypoints LARRE-SHAND-RELIN-25L

I then activate and execute, I then enter the INIT to place all the info as necessary (by click the white tabs to auto set on there) and at 5 degrees flaps. 9 reserve and 80 cost.

I placed the runway altitude into my comm box to 2069', with a runway length of 10526', I then set the radio to 111.75 for ILS, i believe thats right?

I then set on the AP, and take off for FL260 with 250 speed, once off runway I turn on the LNAV and VNAV (auto throttle and flight directors both on) and CMD A

a

Once I get to DAG on my route, the FMC tells me that the plane is set to go to 303/FL260, which it is at that point. Once I pass DAG I set the altitude to 3000 to start to lower, but it does not.

Then when I get to about KEPEC, it says my flight  level should be at 21000 at a speed of around 260. Yet the plane is going at 26,000 still and 303. It does not budge until it gets to around KIMME, where it starts to dip, but by then I am too close to the airport and i get the message DES PATH UNACHIEVABLE. What a I doing wrong??? I have enjoyed this place learning from simple youtube videos and learned how to start it up take off and the FMC, but apparently I cant get it down to ILS approach at 3000 altitude. not sure why!