Typically, when you're deemed a PDT, you get 4x intraday buying power. So if you have $10k cash in your account, you can buy up to $40k of (fully marginable) stock. But that 4x buying power is for the DAY ONLY. You'll need to sell at least $20k of that position before market close (to get back to 2x overnight margin) or you'll get a margin call.
