I have messed up my AVR fuse bits while trying to burn a bootloader(Optiboot). Now my AVR has been bricked. Please suggest any way to unbrick it.

 

Since you have changed your CKSEL bits so that your AVR listens to external oscillator, you need to provide it one. If you cannot buy an external oscillator (note that external oscillator is NOT crystal + capacitors), then use 555 timer IC or you can even use clock of a separate AVR.

 

I had thought of doing that, but I don't know what frequency is set for the external oscillator. Any other way of simply resetting the fuses to default. I'd like to install a fresh bootloader from the beginning as well.

 

If the only problem is that the chip is not set up to use a crystal, then as freak1010 said in post #2, justsupply a clock signal to the XTAL1 input. The signal must switch cleanly between GND and VCC and have close to a 50% duty cycle. The clock frequency needs to be at least four times the ISP frequency.



Another way is to use high voltage programming. An Atmel Dragon will do that but it is a little expensive. There are some less expensive tools that automatically set the fuses to their factory settings. These have names like "Fuse Doctor" and "Fuse Resetter".

 

Thanks for the reference to fuse doctors, look them up and see if they're buildable. My finances are way too restricted!