Toshiba cf2750k

Turn power on and I get a "clonk" sound and the set then imediatly
shuts down. Replaced C840 after the power rectifier right before ic
L78MO5 which is the standby and hold circuit. Also replacedL78MO5. It worked fine until I
powered down and let it sit for an hour. When I then power up the "clonk"
and deadness happens all over again.  Please HELP!!!!!!!!!!!!!!