|I've seen this issue many times. Without knowing more about your computer such as the specs. it would be difficult to pin point the issue. |
Things to try:
You said "i inspect the ram it is ok" I don't know what that means beyond you looked at it. Try reseating your ram all of it. Take it out and put it back in. I have an older machine here that if you move it or let it sit for a long period of time this happens.
You said "i tried another PSU but still no beep and no signal from monitor" This would have been my next suggestion but you've done it so no need to do it again.
Check all connections good. Take them apart and put them back together a few times. Could be a little dust or moisture got in them.
The number of times I have run into this issue when it is not a bad connection it is a bad psu about 70% of the time a bad harddrive about 20% of the time the other 10% has been various things like a bad ram socket or even a bad cpu. A couple times it was a poorly placed metal stand off on the motherboard.