There could be many reasons for this, it could be either a hardware fault or a software fault. Make sure the power is on to both the computer and the screen. Check that there is power to the power point by plugging a lamp in. If this fails a Hamlyn Terrace computer repair centre can help diagnose what is wrong.
You can try installing virus software if your computer doesn't already have it. If you have no luck removing the virus you may need to get your computer serviced by a Hamlyn Terrace repair centre.
The current version of Windows is called Windows 10, it is the successor to Windows 8.
A lot of this comes down to individual preferences. Often a PC will be cheaper to buy versus Mac hardware. Often friends can help you with your computer find out what type of computer they have so that way they can help you with yours also.
Hard drive stores all the information on your computer. The space on a modern computer is usually measured in terabytes which is 1000 GB.