Final answer:
The most likely cause of the computer repeatedly beeping when attempting to power on is RAM not seated properly.
Step-by-step explanation:
The most likely cause of the computer repeatedly beeping when attempting to power on is option C: RAM not seated properly.
When the RAM (Random Access Memory) modules are not properly inserted into their slots on the motherboard, it can cause the computer to beep repeatedly and fail to start up correctly.
To fix this issue, the customer should turn off the computer, unplug the power cord, and open the computer case. They should then locate the RAM modules, remove them carefully, and reseat them firmly into their slots, ensuring they are properly aligned. Finally, they can close the computer case, reconnect the power cord, and try powering on the computer again.