I would check the power supply card first, your probably missing a voltage somewhere. If the power supply card is good, then the next thing in line is the GPU. 

In order to get a chime, the computer "core" is functional. the Firmware boots, the CPU is executing code, and all of its busses are not held into contention by a bad IC somewhere. 

Since there is a chime, 90% of the computer works. However, because of the hard freeze, and now no video, the likely fault here is a voltage to the GPU, or the GPU itself. There are other peripheral devices on the bus, such as IDE/SCSI/USB etc.. that can go bad, but its not very likely. 

The firmware probably enforces initialization of the graphics subsystem, and if it doesnt respond it halts the boot process. Sorta like the imacs plagued with GPU issues, etc... does. 

The chip responsible for refreshing the LCD display itself is still good, or still had power, otherwise the screen would have slowly faded to white after the freeze. 

Now another thing it could be is the L2 Cache could have went bad. It will cause a freeze, and cause the machine not to start if its bad enough.