You are usually forced to "make it smaller." I don't see which i7 but many had onboard graphics so you remove the GPU and test with onboard graphics (again, depends on the i7.)

If that fails you don't need but a few parts to get to the BIOS. BEFORE all the downsizing, get out the DVM and check the CMOS battery. I want to read 3.0 or higher for a pass. Some dismiss this and end up at the shop counter and we check this after a quick visual and the number of times it's this few dollar part is too often. We measure the legs of the PSU at this point too.

Start with simple. Unplug the RESET button just in case it's failed, then test. Nothing? We don't need a lot of parts so the HDD, ODDs and such are removed and you try with a single stick of RAM.

Still nothing? We have to try just the bare minimum parts but at about 3 years and you checked the battery, we remove the PSU and motherboard to a square of cardboard to try a bare power up. If downsized this far you only have a few parts to guess which one.