Zero skycredits


What if my skycredits turns zero but my skycomputer is left on. ? How long will it stay like that?
Will skycredits will go negative?
Or will my skycredits will be deducted next time I pay for credits. Currently my credit is zero and am still in skycomputer. It's saying next sky credit charged in 20 minutes but am having zero credits. My payment bank is in maintainace service so I won't be able to do card payment by tomorrow morning.