Any way to get this sensor working again?

[Lulu]

I'm trying to build a RPM counter using arduino, and to achieve that, I choose to use a simple hall effect sensor together with a small neodymium magnet stuck on a wheel attached to a DC motor.
I'm using the L293D IC to control the movement of my motors. I've tested the hall effect sensor and the L293D separatly and everything worked just fine. Problems began when I noticed that both the IC and the sensor required a 5v power supply from the arduino, and the sensor just doesn't work whenever the IC is also connected to the 5v power supply. I've read many times that this chip draws a lot of power, and I think that maybe that's the reason for the malfunctioning of the sensor. But what should I do? There's any way to get this sensor working again while the L293D is on?

[brad]

Have you tried measuring the voltage of the 5V power supply when everything is running? If the power supply can't handle the amount of current needed by the motors, then the voltage will drop down quite a bit below 5V.