Powering up problems

are there any external devices attached, external storage, mouse, external monitor, ethernet connection etc plugged in when it fails to powerup on battery?
Is there any indication that it is attempting to powerup, the momentary flash of an indicator of some sort?
If neither of these then the battery is flat, faulty or not fitted correctly, changing the operating system is not going to effect the battery.

Since you are asking me and not the original poster I'll share I resolved this on a similar model by changing the boot order. Thanks for asking me.

"hanging the operating system is not going to effect the battery." is false. We know that 7 changed how it taps the CPU so this statement is false.
Bob

we have a language problem here but I stand by my statement that "changing the operating system will have no effect on the battery".
I'm quite willing to be proved wrong but as far as I am aware the power circuits are not controlled by software or even firmware especially when no software is loaded. Software can turn a running system off if the battery charge is too low but I fail to see how it can prevent the laptop from switching on which is how I interpreted the original poster's problem, unless the battery is flat, faulty, or not making good contact ie not correctly fitted. He didn't say windows would not start and he did say it was OK on mains power so there is apparently nothing wrong with windows, but there may be something wrong with the battery circuit.
The comment that the operating system has been known to change something to do with the CPU is irrelevant unless you are suggesting that some change in this area is preventing the "laptop from starting on battery power", because if so why does it not prevent it from starting on mains power?
Finally changing the boot order may cure a problem where windows fails to load but that failure would be occurring on battery and mains power, not just on battery as reported.

The battery times change as we change OS. For example 7 taps the CPU(s) more as we read http://www.tomshardware.com/reviews/intel-core-i5,2410-8.html

This will effect not only the battery but how hot things and if a battery is on the low side, this new behavior can cause one OS to work and 7 to (apparently) fail.

Hope this helps,
Bob

The battery is flat, maybe not completely flat but too flat to start the system, but it would be too flat to start the system even if it was trying to load win xp, vista, linux, or win 7 so the failure to start on battery power has nothing to do with the OS it is trying to start.
I can think of only two ways a battery can perform differently dependant on OS and they are it can flatten it quicker or it can badly monitor the power level so it goes flatter before it switches off but having gone flat enough to switch off it will not matter which operating system it is trying to load, it will fail because it is flat not because it is trying to load windows 7.

Sorry I missed that you might not be the original poster.

See if you can help morse23.
Bob

hey guys sorry i should've said that the starting windows screen comes up but it just sits there at that screen. if i plug it in it immediately boots fully to the login screen. in addition, if i unplug it after it has started and try to shut it down it stays on the screen saying shutdown until i plug it in again. i can hold the power button and force it to turn off but there is some kind of problem with that as well. i'm currently at a different computer right now but when i get back home i will change the boot order and see if that effects it at all. thanks for the advice so far.