iMac wont turn on after Screen Replacement

A quick background. The mac was in working order prior to an upgrade of the Ram and HDD. We cracked the screen and ordered a replacement screen. After trying the new screen before sealing the iMac we noticed it wasn’t turning on. We tried the old screen to make sure it wasn’t defective and the old screen wasn’t turning on either. We tried the following.

• Reseated all the components
• Replaced the LCD display cable
• Made sure to bring old parts from monitor to new monitor

We are getting all five lights(it maybe be 4 lights) on the MOBO when we power on the device. I’m kind of lost what it could be. I’m hoping it isn’t a board or a bigger problem. Any light someone can shed on this would be really great!