Some troubleshooting and possible solutions:

1)hard disk not detected although you installed a new one
Possible solution:
Replace the IDE data cable or the Motherboard
2) The PC hangs when installing windows(OS)
Possible solution:
Format the hard disk drive or replace the hard drive
3) When installing operating system (windows) a blue screen appear with fatal error messages
Possible solutions:
a) Get another operating system to install
b) Replace the CD rom drive
c) Replace the processor
D) Replace the motherboard
4) Several images appears on screen in windows desktop
Possible solutions:
a) Change the no. of pixels and the no. of colors by configuring this on desktop properties
b) Replace the Monitor
c)Uninstall Video Card driver
5)Keyboard functions only on CMOS setup utility and DOS but not the windows
Possible solutions:
a) Apply CMOS clear
b) Replace it with USB keyboard
c)Replace the Motherboard
6) NO display
Possible solutions
a) Re seat the video card
b) Check the memory
c) Check the processor
d) Check the cooling fan if it’s working
If the CMOS setup does not save any changes the battery was defective.