Hold the power button for at least 10 seconds to turn off the PC completely. Then unplug it from the power outlet for 30 seconds. Plug it back in and try booting normally.
it's recommended to contact Alienware support. They can provide more specific troubleshooting steps based on your PC model and error codes (if any). You can find their contact information on the Dell/Alienware website.
Alienware PCs might have built-in diagnostic tools accessible during boot. Try those.