Try resetting the CMOS to set the updated BIOS back to factory defaults. This can be done either shorting the CMOS reset jumper or by removing the battery from the motherboard for about 5 minutes. Please note that by resetting the BIOS back to factory defaults any previous changes to the BIOS will be lost and you will need to enter the BIOS to reconfigure them.
In the event that resetting the BIOS does not help, it may be a bad flash. In this case you can attempt to reflash the BIOS again (with the newer or older version), providing the BIOS is loading an seeking a boot disk. If the computer does not seek a boot disk, then it is a bad flash and there is not much you can do other than replace the BIOS chip or have a repair professional fix it.
Generally speaking, if a computer is running well and has no hardware compatibility issues, then there is little reason to update the BIOS; especially on a big box pre-built computer.