OK, a few things to confirm:
- Are you still using the original power cable, or a replacement?
- If you're using a replacement, what model of MBP do you have, and what model of charger is it?
The reason being that if you're trying to use a 60W power cable (13" MBP) on a 15" MBP which uses an 85W power cable, it will stay on but won't charge the battery as it can't take enough juice from it. Conversely you can use an 85W power cable in any of the MacBooks - it won't do any harm using a more powerful one, whereas it will do harm using a less powerful one.
If it's still the original cable or the right wattage, you might have an issue with the battery. So if that's the case, please can you try the following:
- Reset PRAM
- Reset SMC
If the issue persists, we can download a battery health monitor to check how the battery is. Please quote this if you need any assistance with the above.