loading problem

my project is a "data acquisition system"
where a temperature sensor is connected to ADC-0804,which is connected to 8051-P89V51RD2...and 8051 to LCD-JHD162A to display the temperature....

when i dont connect 8051 or LCD the voltage is shown correct at GND and VCC ie.5V
but when i connect either of them voltage drops to aroung 2.2V and thus both dont work..
there is no problem with ADC bcos voltage with and without ADC is correct(5V)

i have remoed almost all other components to find the fault..
can there be a problem in crystal?

plese help...

Start with just the 8051 in the circuit. Get that working first. Then add the LCD. When that works add the sensor.

When a device draws too much current the supply voltage drops. I expect you have one or more wiring errors. Or a very current challenged power supply

A schematic may help. Is this a board you wired or etched? Schematic.