I left my Lenovo laptop untouched for two weeks, and now it won't hold charge?

Remove the battery for a while then replace it and charge it again…

Charge it with the laptop off. Then turn it on and deplete the battery without charging the battery. Charge it up to full AGAIN and you have just "re-calibrated" your battery. Hopefully it will hold a charge properly now.
If that doesn't work, then get a new battery.