Put the key in and turn it to the ON position, and let it sit for 5-10 seconds. Then turn it to the START position, and try to start it up. Sometimes the ECU needs to re-initialize the ROM after flashing, and starting up a freshly flashed car can cause exactly what you're seeing. Did the flash complete 100% successfully?
If that doesn't work, I'd check your battery. It sounds like it might be dead, especially since you're only seeing 11 volts. Should be 12 while off, and 13.x or so when running I believe.