Why are you burning a bootloader on an ATtiny? The normal approach is just to upload programs to it via ICSP.
Using the burn the boot loader option in the arduino IDE sets the fuses which determine the micro controller clock source. Factory settings run it at 1MHz so to run at the faster internal clock of 8 needs this step. By selecting an external clock source like the OP did in error the uC becomes unresponsive unless an external clock source is provided.
Same thing happens with the ATMega328 when setting up a standalone board - once the Arduino UNO boot loader is in place the fuses for an external clock are set and you can't get a reaction from the uC without an external clock signal of some type.
Difference here is there's no boot loader as such, so that process only sets the required fuses.
Edit: fixed poor punctuation and spelling.