Dell Studio 1537 won't turn on

I'm sure you all have had this question asked dozens of times, so please excuse me. I bought a Dell Studio 1537 a little over a year ago. It has worked great up until two day ago. After getting home from work two nights ago, my computer would not turn on. Noo lights flashed, no startup noises, nothing. After monkeying around with the battery and the power adapter I finally got it going like an hour later. Once I turned it on the battery had nearly full life, that wasn't my problem. Same thing then happened last night. This time no amount of messing with the battery helped and I ended up removing and replacing my memory card. After which it booted right up. Tonight, once again nothing happened and this time neither of the previous procedures worked. So this time I ended up pulling the hard drive and plugging it back in and the laptop booted right up. Any clue what the problem might be? Once I get the stupid thing running I have no problems. However, it's not starting up when I get home at night. Thanks!