Possibly Static damaged the old ram.
Also did you remember to turn off the mains and wait a few minutes for the capacirots in the PSU to discharge before you took the ram out?
Another idea, could you have accidently dislodged the power cable for the CPU fan?
OR perhaps have a cable jamming the fan? If the mobo has fan speed monitoring, it may have noticed the CPU fan is not spinning, hence the beeps, and once the CPU gets too hot, it shuts down the PC to avoid damage.