Your PSU only has 168W on your 12V rail, the 8800GT has a TDP of 105W, leaving your CPU and everything else that needs 12V power less than 65W to work with, thats no good, it will probably stress your PSU out and kill it, or it might not boot at all.
Worst case scenario, the PSU goes out with a bang and kills all of the other components in the system with it. Most likely scenario, it slowly stresses, goes out of spec, and shuts of your system at random times and will eventually refuse to boot.
I would NOT try that. Not enough power to be safe. It may just not run, if its really not enough, but it might run, being on the edge of enough power. If you run it on the edge, you are risking it blowing out, which could do nothing, but could also damage other parts of your PC. Definitely not worth the risk IMO. I'd get a bigger PSU and be safe.
Ohhh. Thanks for the fast reply and help guys really appreciated.
But I got more questions
How many Watts is available if I remove my Old Graphics card?
Any video cards recommended that will match my PSU availability?
Also I found a thread that have same problem with me same PC and same Power supply
He said he tried out GeForce 8600 GT and it run well no problems in 2 years
It does not matter how many watts you will have available if you remove the old one. You will still not have enough for an upgraded system to run reliably.
What do you want to do with your system? Any modern graphics card will require at least a generic 350W as a minimum to be able to run your system without problems.
The 8600GT does not require a dedicated power cable. The 8800GT that you are looking at does. And as a matter of fact, most modern graphics cards dedicated for gaming will probably require that cable too.
If you want to do some gaming, don't think about it, unfortunately you will NEED to upgrade your PSU.
Think of your PSU as the wheels of a car. It does not matter what sort of car you have up there, even a Ferrari on wooden wheels will not be able to speed more than 20km/h and it will not do so until it soon breaks down! Better to invest in a good quality PSU and have piece of mind.
+1 to darkguset. You really need a new PSU to upgrade your GPU. Its worth the money in the end anyway as a good power supply that you get now is the type of thing you can transfer to your next rig as well. Doesn't have to be super expensive or huge either, but a good quality 400-500W + PSU (can be had for ~$50 +/-) will run most graphics cards out there right now, outside of the dual GPU type cards. Its a worthwhile investment.