Hi @Peter Bailey
Bit confused.
Which PC now failed? The original or the new one?
Why did you swap HDDs?
Did the new PC work with its' HDD?
If it did but not with the your original one there may be a software problem.
What OS is installed?
Can you start the PC without the HDD connected?
Have you tried a power refresh? Most motherboards have a CMOS battery (usually coin cell but maybe in your case, not cannot even find a user manual for your model) See the procedure in the Most Helpful Answer above.