I've seen the craziest things, keep a new build from booting.
Like the psu set for 220v instead of 110v. I can guarantee that, if the PSU came from S. America or a dealer who deals with S. American countries.
I used to buy PSU's from a wholesaler in Miami, and every one of them was set for 220v operation. The switch is on the back of the PSU, next to the power input socket.
On a new MOBO, I've seen the CMOS shorting jumper in the SHORT position, and a blocking tab under the CMOS battery.
All of the above, take only a few seconds to check.
The problems just go on from there. If it can go wrong, I've probably had it go wrong for me, sometime in the last 33 years since I built my first XT Clone.
Once a guy learns all the little pitfalls, in building a PC, and learns how to avoid them, a new build can take less than an hour and run correctly on the first Power Up.
Good Luck,
Shadow