Could front panel connections damage my motherboard?

I just built my first PC. Things have not gone well to say the least. The case is an Antec 900 hand me down from a friend, but it is in good shape. I assembled everything out of box first and it worked. I assembled everything in box and my motherboard (Asrock p67 extreme4 gen 3) fried. I could not find a reason why and just figured I made an error somewhere. Amazon sent me a new one. When that one came in I assembled out of box again and it worked. When I assembled in box and powered it up, it fried again. Both times there was actual damage to the back side of the board. Amazon would not send me another, so I bought one. When it came in I spent hours making sure everything was perfect before powering it up. When I pressed power same thing happened only this time there was no noticeable damage to the board. I removed it and did an out of box set up and it still worked. I took my time reading forums and trying to figure out the problem. I decided to mount the board in the case and attach all my essentials without attaching the front panel connections (Power, Reset, HDD LED, USB, 1394, and Audio). To my surprise everything booted fine. I know that all the connections were in there right places, but after reading some forums I realized my HDD LED may have been attached backwards. I also cleaned out all the dust from the case with an air compressor and air chuck when I first got the case, which I have read is a no no. So here are my questions:

1. Could the HDD LED connection have damaged my board and if so is it safe to plug in my other header connections?

2. Could cleaning the case have damaged the wires and caused the damage to my motherboard?

3. Is it safe to just use my power and reset? I would rather not buy a new case if I can help it and I am too scared to try now that everything is running.

4. Would a new case work now or could the motherboard be too damaged at eh header connections? (there is no visible damage)

I would like to point out that everything is working fine now that the front connections aren't made, so standoffs, PSU, basically all other components aren't an issue. Thank you for your help.