Are PCs manufactured to be operated in Japan safe to operate in the
U.S.? I want to know if there is a product or procedure I can do to
convert it to U.S. voltages. I want to know if it will explode or burn
if I plug it into a wall socket.

I have had no problems with using Japanese PCs in the United States. 
As indicated on this website:

http://users.pandora.be/worldstandards/electricity.htm#voltage

in Japan and in most of the Americas the voltage is between 100 and 127 volts.

As the previous user posted, there usually is no problem.  However I
wouldn't reccomend using a plug and pray attitude.  Find what type of
power supply you have and get a copy of either the user manual or a
detailed specification sheet from the manufacturer.

There's two items you want to locate:
First: Input Voltage ( USA uses 120V -- general ranges are 90V-130V
[or VAC--same thing] )
Second:	Input Frequency Range ( USA uses 60Hz--general ranges are 47-63Hz)

Once again though I would stronly reccomend you check your individual power supply.

Good Luck

Japan's got some funny electricity issues due to historical factors. 
Western Japan, from the Kansai region westward, runs at an AC
frequency of 50Hz, while eastern Japan from the Kanto east runs at
60Hz.  Manufacturers in Japan have had to figure out how to make
products that sell nationwide without going funny, and consequently,
Japanese appliances and other electrical products are usually better
at handling variations than similar products made in the US.

However, I would definitely follow brian_m's advice!  Get whatever
details you can for the power supply and see if US voltage will work. 
I had no trouble taking my US PC and using it in Japan, but then I
checked the details sticker on the power supply before I got there to
make sure.

Cheers,

        Eirikr

I bought a couple of Dell computers in Japan. I have had no problem
using them in the US. In fact, Dell has said they will give customer
support for the Japan bought laptop in the US. Which is why I bought
the Dell. We have been using one of the laptops in the USA since
March. But, something to consider is the long term effects on the
power supply. Maybe the unit will not last as long as a US system for
the reasons stated above about voltage and cycles.