Can a bad RAM stick stop a computer from starting up?
Can a bad RAM stick stop a computer from starting up? When I power up all the fans and driver run.
Best Buy checked the power supply and it is ok.
Yellow light below power button comes on for a couple minutes. no beeps though. Monitor says power saving mode and goes blank.
Checked out hard drive in a box on the lap top it is good all the files are there. It acts as though it cant find the system bios to start up the OS.
Can a bad ram stick cause this or can the processor find what it needs to run directly from the hard drive?
MacBook Air's have soldered on DRAM are you sure you have a MacBook Air?
The MacBook Air's do have replaceable HD or SSD units (depending on the model). But given your symptoms it sounds like you have a battery or EFI firmware issue.
It would be helpful if you could supply us the last four digits of your serial number so we can correctly identify your model as well as what OS-X you are running.
Yes. Best Buy should be able to run AHT on it. If they can't (don't know why they didn't) then you may have logic board problems. Each machine goes through a POST (power on self test) that's when the EFI (mac for BIOS) checks and reports hardware errors (though sometimes the is no error code for the problem e.g. too much current draw).
Disconnect all peripherals before attempting to boot.
If this answer is acceptable please remember to return and mark it.