|Electro-Static Discharge can damage sensitive electronic components. If you had a static charge on you body and it discharged into the components they may have been damaged. |
This doesn't happen too often but is something that has to be taken into account. If you are located in the northern hemisphere the cold weather can cause low humidity indoors, which can propagate ESD.
There is no practical way for you to check for this damage. What you need to do is go back through all the steps you can take and eliminate them as causes of the current condition.
The best way to check connections is to actually take them apart and put them back together.
IF you removed more than one connection at a time, it is possible you reconnected wrong.
If you disturbed the CPU cooler the computer should try to start but may immediately shut down. In that case, the cooler must be removed. The old paste/pad completely cleaned off using approved methods and then new thermal paste applied according to instructions for your processor type.
I suggest you disconnect any and all external hardware other than your monitor and keyboard. Unplug the power and data cables for all the drives in the case including the CD drive.
Remove the memory modules and reinstall ONLY one stick in the first slot. Snap it in and out 4 or 5 times to burnish the contacts.
Remove the add in graphics card. remove any memory cards, floppy disks, flash drives, external drives, cameras, printers, etc.
Leave the side cover off and watch for any signs of life when attempting to start.
With the hardware I have described connected you should see the computer POST to a screen saying do boot/system device found. If you get to that point then post back for more help.