The suggestion in Mark D's answer is a good one as it helps you eliminate one very obvious possibility, although it's not clear to me whether you may have already tried this as you state I also tried using the SSD/HDD but it still won't turn on.
Although you're not sure whether the physical power button is faulty, I would still try resetting the SMC to determine if this has any impact.
It's not clear which 2009 model MacBook you have, as some models had a built-in battery and others had a removable battery. Below are instructions for both scenarios - so choose the one that applies in your case!
Built-in battery instructions
- Shut down your Mac
- Unplug the power cable from your Mac
- For 10 seconds, press and hold at the same time the shiftcontroloption keys (on the left side of the built-in keyboard) and the power button
- After 10 seconds let go of all keys and the power button
- Plug in the power cable
- Turn your Mac back on with the power button.
Removable battery instructions
- Shut down your computer
- Disconnect the power cable from the computer
- Remove the battery
- Press the power button for 5 seconds and release
- Put the battery back in
- Reconnect the MagSafe cord (or power cable)
- Turn your computer back on with the power button
Once you've taken the appropriate steps, see if you can power up the MacBook. If you can, I would then also reset the NVRAM as follows:
Reset the NVRAM
Older Macs had what's called Parameter RAM (PRAM), newer Macs use Non-Volatile Random-Access Memory (NVRAM). Here’s how to reset this in your MacBook:
- Shut down your machine. Yes, a full shut down, not just logging out.
- Press the power button and then press the commandoptionpr keys. You have to make sure you press these keys before the gray screen appears or it won’t work.
- Hold those keys down until your Mac reboots again (i.e. a 2nd time) and you here the startup chime.
- Let go of the keys and let your Mac reboot normally.
Note: When you log back in you may need to readjust some of your system preferences (e.g. speaker volume, screen resolution, startup disk selection, time zone information, etc).
After trying the above, let us know how you go.