Hi Mr_Kangaroo.
There are two methods of starting the b757.
Method one by APU.
1) select batt to on
2) start apu,and wait till it fully runs up
3) then the apu electric gen will be on line
4) goto packs panel,make sure the packs are OFF
5) at the bottom of this panel select the cross feed s/w to OFF
6) select the APU valve to ON
7) select num 1 left eng  valve to ON
8) goto start panel,make sure both start s/w`s are in the OFF position
9) then turn the num 1 left eng start s/w to  GRD
10) you will hear the eng start to turn over
11) goto eicas and wait till the num1 left eng inst starts to rise
12) turn on the num1 left fuel valve on the pedestal to on
13) let the left eng stabalise
14) goto aircondition panel and select crossfeed valve to ON
15) select num 2 right eng valve to ON
16) goto start panel and select num 2 right eng to GRD
17) you will hear the num 2 right eng start to turn over
18) goto eicas and wait till the num 2 right eng inst starts to rise
19) turn on the num2 right fuel valve on the pedestal to on
20) let the right eng stabalise
21) goto eng start panel and select both eng start s/w` to the cont position
22) APU can now be shut down,and air packs can now be select to ON

Method for ground start
1) GOTO the captsim caption at the top of the screen if you are not in full sceen mode this will be visable,if you are in full screen mode then you will have to do the same as you would if you wish to select fs9 flight plan to bring the menu bar at the top of the screen,then select ground power for the electrics,then do the same again but this time select air ground cart for the air supply.
Start proceedure is the same as above except you do not need the APU start and shutdown bits.
Instead you select the ground power s/w on the elect panel to on
regards alan.

It's really works?

Javier Linares