PC won't turn on after cleaning

Remove everything but the motherboard, cpu, memory, and power supply. If it turns on, put in the GPU and if it still works, reconnect your hard drives.

 

Do what above poster said.
Personally when I had this problem, I had to reseat my gpu and network card. Blowing out dust while they're disconnected first. Seems that dust got blown into the pci slots and was causing problems.
Also if your mobo gives you beeps on startup, look online for beep codes for your mobo.
If nothing works still and you want a sure diagnosis, use a POST tester. They're fairly cheap

 

If it's anything like my Asus mobo (don't have time to check whilst at work) then A0 is its normal operational state. That means it's probably something to do with the graphics card.

As above, reseat the graphics card and see if it works. You can also try plugging the monitor into the integrated graphics ports on the back panel of the motherboard. If that doesn't work, try clearing CMOS and trying again (there might be a button on the MoBo or on the back panel that makes it easier).

 

According to the user's manual for your motherboard A0 seems to indicate that it's started initializing IDE. I'm not completely sure what that means in terms of whether or not it's working alright or not, but it could be worth having a look at IDE/SATA cables to see that they're connected properly.

Edit: Obviously you should try to get a picture from your GPU first (onboard or other).

 

Sometimes dust and dirt can prevent contact on a pin on one of your components. There are a lot of pins and just one of them needs to fail so problems like these aren't too uncommon.

Also, that seven segment display is a Dr.Debug and displays a different value depending on what the problem is.

 

In general, one of the best things to try when you detect unexplainable behavior is to completely unplug the computer (including power, Ethernet, video, etc.) and then wait up to 30 minutes. Once you are done waiting, plug everything back in and try the system again. Sometimes, various components in a computer can have bad voltage levels and you need to full power off the system so the capacitors can completely discharge. Also, some systems (although I've only seen it in laptops) have a safety feature where if anything problematic is detected, the system prevents booting for either a set period of time or until a particular component has been removed and re-seated.