Are you using the same MagSafe power adapter that the system came with? The early 2008 MacBook Pro needs an 85W power adapter to work properly. If this isn't the original power adapter, check it to make sure it is 85W. Some MagSafe adapters, especially ones built for the MacBook Air, may not provide enough power.
It is also possible that your power adapter has failed somehow. If your power adapter is 85W, try charging your computer with another power adapter.
The Power Manager in your notebook can cause strange power behavior like this, and it may need to be reset. To do this, disconnect the power cord, remove the battery, then hold the power button for at least 5 seconds. Then reinsert the battery and reconnect the power cord, and check whether the problem has been resolved.
It is also possible that the PRAM has become corrupted or has bad settings, many of which you cannot access directly. You can reset the PRAM to its default settings without losing any data. To reset the PRAM:
- Make sure the computer is shut down and plugged in.
- Press the power button and immediately hold down the Command, Option, P, R keys simultaneously.
- Hold the keys until you hear the startup sound a second time.
Apple Hardware Test
If the problem persists, you can instruct your MacBook Pro to perform a full self test to try to determine the problem. To do this:
- Disconnect everything connected to your computer, leaving only the power adapter connected.
- If the computer is on, shut it down.
- Turn on the computer while holding the D key down.
- When the Apple Hardware Test chooser screen appears, release the D, then select your preferred language.
- Press the Return key or click the right arrow button.
- The Apple Hardware Test main screen should appear in about 45 seconds. When it does, follow the onscreen directions.
If the test detects a hardware problem, it will display an error code. If it displays an error code, write it down. Call Apple support or bring your computer to a Genius Bar, and tell them what error code you received, or search for the error code online.
If you cannot find the answer yourself
If none of the above steps solve your issue, the best thing to do is to call Apple or visit a Genius Bar.