System wont run after cleaning heat sink and fan.

I'd start with removing the CPU again and taking a look to make sure you didn't bend/rip off any pins on the CPU (although if it's a newer intel setup that wouldn't be the case 775 and on don't have pins, however they also tend to have actual hold down brackets so I doubt that's the case... but anywho) Oh and be careful when you're removing the heatsink, the easiest way to do it, is to make sure your computer is running, get the thermal paste nice and warm so it's actually a paste and not like glue. Turn the computer off, unplug it and then while still a bit warm, twist the heatsink while pulling out. Be careful, you can do some serious damage to a CPU when pulling it out with the socket still "locked"

Sometimes, when you pull out cables or components from your motherboard, other items get loosened. If you say you can hear your processor working, then try to replug your video board or video cables. Make sure to have proper grounding when removing and plugging boards in. You can also try to press down on your processor while it is running to verify if it is a contact problem that you created when you removed it. Hope this helps.

I'm not sure that I would have removed the heatsink at all! I would normally just use one of those cans of compressed air just to spray between the fins on the heatsink and this would normally suffice. It sounds like you may have accidentally caused some damage to the processor. It sounds like you may have zapped your processor as a result of static electricity. It's very dangerous to handle computer components without properly grounding yourself first. The processor is an extremely sensitive computer component when it comes to static electricity. I think if you tried replacing the processor back in the socket and then replaced the heatsink and everything is tight then it should work. If you aren't seeing on your computer then you have a major problem. You may need to replace the processor although I would take your computer to a local technician for further advice. I remove the cover on my own pc on a regular basis and I make sure that I get rid of the dust from my heatsink but I never remove it. I really wish you well with this. Andrew

i also do not have any idea but when i have a problem with my PC i go directly to technician to have it checked

in my opinion you already damage the processor since according from you,you separate the heat sink and processor chip with pressure,possible cause to have scratch the top surface of the chip and prone from some static electricity.

Not sure why you would want to remove the CPU/and heat sink, for future reference you will want to use can of compressed air, as even just a basic static discharge when you touch the CPU could fry it. I like the fact you were brave enough to open the case and get in there, but next time you should try to read up on it first before getting your hands inside the computer. Those electronic components are fagile and can get damaged real easy. Hopefully a new CPU will not be too much more.. you might have a hard time finding a CPU replacement as there are new CPU's out now..

As you say after cleaning heat sink and fan your computer wont run.. I think any wires are loose in your CPU or any wire which connects hard disk to motherboard called sata cable.. you can check this cable.. it is properly connected or not with board..