+5v supply should never drop below about 4.95v, so you've got big problems. Try disconnecting the power to some of the devices (usb, cd, hd, etc) and check your bios reading again, if it is still low disconnect everything except the mobo and check again. If it is STILL low, get it checked with a meter, and if it is actually that low there's a fault, either your mobo is drawing too much power or you ps is faulty.
If the voltage goes up when you disconnect some devices, you need a better ps, and pretty soon too.
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