My monitor has a problem, everytime I install a new game or everytime I open a software (which takes a lot of RAM), play some games ... the monitor changes to black and the "No signal" appears on the monitor.
I did check the monitor caple, and put monitor caple in another wall plug, but it does not stop.

Please help me!

My system information :

RAM : 1GB
Window XP Home Edition (5.1)Build 2600
Direct X 9.0c
RADEON 9200 Pro 128mb
Monitor plug and play

This seems like an issue with your computer, where the system shuts down or the graphics card dies when the computer is put under heavy load. I recommend updating your video card's drivers, found at this page here: ATI Graphics Driver.

If possible, try a different monitor or video card to experiment with configuartions.