More info required. If it is not making any noise at all when you start it up, then it could be that the power supply is broken. If it partially boots up see if you can get into safe mode.
When most computers have a hardware failure at start-up they release a series of BIOS "beep codes", if you're hearing any beeps at start-up, Google your computer's manufacturer and model along with "beep codes" in the search field and try to diagnose the problem that way. If the power sending unit is broken, (on most new power supplies) a small LED light will blink. Your power sending unit will be on the back of your tower where the power cord is plugged in. Hope that helped.
i have faced this problem too... consult a computer technician. there is just problem with your RAM....hard disk. just get the cpu cleaned and ram changed
You really need to learn to diagnose these issues; First ideal every assumes it can be 'Windows'. Does your computer power up? Do you see anything with on your monitor? If nothing is on your monitor, but the PC powered up - this could mean; Monitor died; Video Card died, If video card died and it's on board, don't worry, don't replace the whole board - just find an inexpensive video card that supports your computer. (Most commonly now, you need PCIe) - If you get an high end video card - you might have to buy a new power supply as certain amount of AMPs are required. Before we go into all of that; This could be a simply lose cable on the back, make sure they're connected, including the power cords in back of the monitor as well. If all checks out; Try a different monitor if you have one, in fact if you don't have one, but do have a laptop, hook up your monitor too the laptop...does it turn on? If that works, we know it's not the monitor. Since you said it's a blank screen this could mean that it's a memory issue; Turn off your computer open it up; Pull out all your memory and put in one stick at a time; Power it; Does it work? If yes, try doing this until all ram has been well-seeded into place. If you get the same blank issue, the issue is obviosy, you have a bad stick of ram - If lets say 3 sticks of ram work and the last one you put in doesn't then that could mean it's bad stick of ram. Try taking the supposely bad ram and placing into a working memory by taking that one out. Does it power? If so, the ram isn't bad, the specific slot is bad - and can't really fix that and a new motherboard will be required at this point. If that ram does fail, in a working slot from the other ram, then put the other working ram back...and take the bad ram and take a number 2 pencil and simply erase the gold plated edges on both sides, this sometimes correct these issues (Done this many times and has worked) If you're getting the same issue on any of the ram, either the motherboard is completely shot, memory is bad or it's more than likely something else. There's a lot of possibilities that can cause this and if you're unsure, It's recommended find a computer savvy friend or take it to a local computer shop.
For things like this you need to be more descriptive and moreover a person really should be there to look at it. Unless you are computer savvy this is a problem best resolved with a technician there with you.