Power Problems on Dell (No Boot)

I have a four year old first gen XPS laptop, if that's important.

The problem is as follows (The primary battery is out, computer connected directly to wall via AC)
-I tried to turn on the computer after normal use, and there is no activity, except the three lock lights (Caps, Scroll and Num) come on, as does power light for about 5 seconds. The fans don't spin up, the hard drive has no activity, nothing at all.
-I tried reseating the ram (this worked once before) no luck.
-If I hold the function key for five seconds, then continue holding and press the power key, only scroll lock light and the power light go on for a few seconds and turn off. Apparently this is a code, but I don't know it.
-I used another power cord to check that wasn't the problem, it wasn't.
-I completely disassembled my computer out of lack of other options/curiosity and remembered the reserve battery on the mother board. I disconnected it, reconnected it and rebuilt the computer.
-Without the primary battery in, but with the computer plugged in, I get a flashing orange light on the battery LED. If I then put in the primary battery, the flashing light goes slower and to green color.
-Then the system will boot up to windows, after I input a BIOS time.
-If I don't do it in this order, say I put the primary battery in before connecting to AC, it won't boot.
-After I had windows running and everything working normally I shut down.
-The same boot problem happened, meaning I had to disassemble to the point where I can access the reserve battery again.

I think there must be some kind of power problem, but I'm just don't know what or where, and dell's tech support (both phone and online) has pretty much said, buy a new computer.
If it's something I can fix I would like to.

Thanks in advance to anyone who read all that and extra thanks to anyone who can offer me help with this, if there's any more information that would be useful, please let me know.