connecting more than one Lm35 sensor to ADC pins of Atmega32 micro-controller in Proteus software
Most of digital ICs (MCUs, logic gates etc) in the ISIS library have hidden VCC/VDD pins. By default, they are not shown in the schematic but are designed to connect automatically to POWER terminal (the terminal with the up-arrow symbol). Yeah, it's 5VDC but it's not suitable for powering analog ICs like LM35.

Replace them with a "DC" source. You can find it under GENERATORS group to the left (the circle with a blue sine-wave symbol inside it). Place one, double-click on it and set the voltage to 5.

Note that if you're planning to transfer this circuit to ARES for PCB design then it will be problematic because of that POWER terminal.