It's hard to say, but it sounds like you damaged a number of components while doing the top case replacement. As you're no doubt aware, this involves removing the display assembly, and the logic board, so there's ample room for introducing ESD damage if you're not careful AND know what you're doing.
Without seeing the environment in which you were working, not to mention watching you actually do the replacement, it's impossible to say whether or not ESD damage is likely.
In any case, here's what I'd do. Start by removing the battery and see if the system will power on with the AC adapter alone. If it does, you probably just have a bad battery or you didn't get the battery connection cable in properly. This is one of those cables that runs under the little retaining wall between the logic board and battery/HDD and is in the gap for the locking level on the bottom cover (not the battery cover).
If it still doesn't work after that, you could try removing the logic board and making sure the magsafe board is fully seated in the connection slot, but there was really no need to ever disconnect this from the logic board if you're just doing a top case replacement. But if it's not working after you take the battery out, then the odds of damage to the logic board just went up to near 100%.
To put it another way, based on your description so far, I'd say the most likely scenario is that you damaged the logic board. Nearly every time I've come across a system with similar symptoms as yours, it's the logic board that ends up getting replaced. And the fact that you did this little operation on your own, means that you're going to pay significantly more for someone to fix it. Probably a lot more than the cost of a new system.
The logic board alone, and strangely enough it doesn't seem to matter if yours is the 2.4 or 2.5GHz model, will probably be around $1,000 all on it's own. If it's the 2.8GHz model, that adds about $300 to the price. There's a good chance you damaged cables that are part of the display assembly, so that's at least another $500, then there's the airport card which could be bad, and whatever else may have been damaged, plus labor... You get the idea.
If I were to speculate on what was happening before... You probably damaged some resistor or capacitor related to power distribution. So even when the system said it had a full battery, it was probably running off of battery power. The SMC was probably just confused because it could detect that you have the AC adapter connected. You might have even been supplementing the battery power with a little AC power which allowed you to run off battery power for much longer than normal. But once the battery power ran out, there's not enough AC power to get the system going. If you charged the battery via other means, you may be able to run the system again, but essentially it's ability to charge the battery and run on AC power is mostly likely permanently gone.
In the future, I'd suggest taking your system to a professional, or get some old crappy systems to hone your skills on. And just a few tips to help speed things along:
1: Always make sure to ground yourself. If you don't have an ESD wrist strap or anything like that, find a metal surface to touch.
2: Don't work on any kind of carpeting or linoleum. Both are great for helping you build up a static charge.
3: ALWAYS handle PCBs by their edges and avoid touching anything that is protruding from the board.
4: Do not carry PCBs any more than you have to outside of an antistatic bag
5: NEVER place a PCB in anything OTHER than an anti-static container.
And all the other Working with Sensitive Electronics 101 stuff that I didn't mention.
I respect the people at the iFixIt site, which is most likely where you found the instructions on how to do this procedure, but they often assume that you have some basic knowledge of how to work with electronics. Most people don't. Odds are you're one of them, and you've now joined the ranks of those who have destroyed their first bit of electronics. We've all been there. A few years back, I was trying to change cases on a custom built system of mine... I was in a bit of a hurry, and neglected to put in the standoff screw mounts in, leaving all the solder joints on the motherboard touching the bare metal of the case. That was a good learning experience for me, like this one can be for you.
I have just replaced the keyboard and top case on my unibody MacBook Pro 15" (A1286) late 2008. Prior to this, only the keyboard/backlight and Superdrive were faulty.
After switching on for the first time, the keyboard and backlight worked perfectly. However I noticed the following new faults:
1. Airport not installed error message.
2. Bluetooth could find devices, but not pair with them.
3. Magsafe charging light didn't work and battery didn't charge. However, the battery indicator light showed a fully charged battery.
At this stage, I reset the PMC and SMC. I couldn't run the Apple Hardware Test, as my DVD drive was dead. Despite these faults, the computer worked perfectly when plugged into the mains. Yesterday however, I used the computer on battery and allowed the battery to drain completely. Now the computer will not turn on nor charge the battery. The first battery indicator flashes for 5 seconds when the charger is removed. Otherwise the computer is completely dead.
Does anyone have any ideas? I have re-checked all the connections to the logic board and everything is correct. Is the fault likely to be the battery, DC-in board or the logic board? I have determined that the charger isn't at fault as it works on another MacBook. I don't have access to a similar MacBook, so I'm not able to swap batteries.
Help would be much appreciated as I refuse to believe that my much-loved mac is dead, seeing as all I did was to let the battery run dry...
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