How can i know when to stop overclocking.

when we mean : unstable, it's your computer's which have crashed, made blue screen of death, restarted.

If you want to know if you computer's is stable, download OCCT and if the test is done without error, your system is stable and you will be able to o/c more.

Could you tell me about CPU, Power supply and motherboard and I could answer your question.

There is a lot of tutorial about o/c you should look at these

Most people realize it by their third RMA.  

Sorry I couldn't resist!  

You stop overclocking when you've reached the highest STABLE overclock your hardware can run with the cooling solution you have.

i want to overclock i7 860 with 500 watts psu and asus maximus III formula with zalman cnps10x performa. i have gts 250 1GB graphics card.

Do i need more power supply?

You have got a great configuration  
About your PSU, it depends of the brand (corsair, be quiet, Antec...) using. If it's noname PSU, you could meet some problem as unstability, BSOD or other...
Even burn your PSU along with some composants (Perhaps MB, GPU or nothing)

So what PSU's brand do you have ?
Thx

i am using corsiar

OK, your PSU are going to suffice, corsair is a good brand, I have got a corsair HX620 Watts (I won it in contest) and I o/c my core I7 920 at 3.4 ghz. you will be able to o/c like you'll wish it.

You asked me : Do i need more power supply?
The answer is : No He needn't more power supply.

thanks. is it ok to go 3.8 ghz on this power supply

Best answer selected by ruffandruff.

thank you soooooooooooooooooooooooo.................................much. it help me a lot.