You should see boot messages and stuff over HDMI. Here is the LED sequence over boot. Can you compare these steps with what you see over HDMI? Even with no USB or SD connected there will be HDMI display for the bootloader eeprom.
The green LED on the front of the Raspberry Pi will go through the following sequence after power-on:
- RPI EEPROM booting: solid green (~5 seconds)
- U-Boot booting: solid black (~5 seconds)
- Linux Kernel booting: solid green (~5 seconds)
- OS booting: black flashing green (~10 seconds)
- Waiting for NTP time sync: green flashing black
- DVR active: solid green
The DVR web interface on http://dvr-server is accessible as soon as the OS boots (step 4), approximately 25-30s after the Pi is powered on.