Why when turn on computer there is a sound signal from computer but the monitor has no picture but monitor is okey.

IF THE MONITOR IS OKEY IT LEAVES THE VIDEO CARD.
REMOVE THE VIDEO CARD CLEAN IT RESEAT IT.
USE CANNED AIR TO CLEAN IT WITH GENTLY.
THE CABLE SHOULD BE SEATEN FIRMLY AND FAST.

Check your cable connection on both ends. Try to change the cable.

This sounds like a dead motherboard.
you should reset the cmos (using a jumper) or remove all power cords, battery and the cmos battery. wait 10 mins and put everything back.

The second option is a dead power supply. The only way to check that is to replace it with a new one.

I would bet on some component(s) have become thermo sensitive. Most of the time capacitors can do this type of thing. Most likely the defective caps could be in the power supply.

To locate the defective caps, you would have to be able to run the supply and use the combination of a heat gun and freeze spray (liquid air spray) for cooling. At the same time you would have to monitor the output of the supply to see the components that cause the output change.

It is also possible to have thermo sensitive components on any of the other boards. This would also require proper troubleshooting.

The service rep would replace boards until he found the defective board. Then he would return the set with the new board and the bill for his work.

If your set is out of warranty, it may be better to consider a new set. Servicing these can be fairly involved and expensive.

Jerry G.

Not sure this will help but it sounds like you might have PIP (picture in Picture ) turned on

check all your cables leading from the computer to the monitor. the clicking is normal as the monitor looks for a signal from your computer, if it finds one it locks on. if it doesnt find a signal it clicks again going into standbye mode. the fact that its clicking shows its trying to find the signal.
the cables may be loose. the computer could have a setting too high for the monitors refresh rate.
do you see anything when the computer starts? or just a blank screen saying "no signal"?

Remove and reinstall memory.

No. HDMI transfers picture and sound, but DVI does not. You need a audio line as well.

Have you checked your connections inside the unit?

tell me if there is something i need to know like: what were the things that you've doing with your computer before the problem happened?? are there any recent hardware/software changes?? tell also your OS- is it XP or Vista...
1

first, let's try to check if the problem is with the monitor or not,okey? try unplugging the monitor blue connector at the back of the tower.and make sure that your monitor is turned-on.If you can see a colored bars displayed.you monitor is okey.if not, try a known good monitor...if it woks the problem is with the old monitor.(resolved)

2 (if not)
Now, complelely turn off your computer and try reseating all the cables, and your hardware components such as memory,video card,IDE cable and so on. but before doing so, unplug the power cable and then push the power button to drain the power.after reseating everything, plug back the power cable and turn on computer.try listening to the tower,tell me if you can hear some beeps also.

if no video issue is still there, try putting a known good video card if you have any.if a known good video card works then the problem is with the old one..

if the problem is still there after everything that you've done try calling the manufacturer. this is lead to a motherboard problem but try to call them first.