New computer won't display anything, still powers on

Hello!

I bought a Gateway DX4375-UW20 a few weeks ago from Walmart for school, MS Word/PowerPoint and "light" gaming. The problem addressed in the title occurred just after I turned back on secure boot after previously turning it off in the BIOS... I pressed F-10 to "Save and Restart" BAM, never booted again/or got the bios screen either. I also do not get any USB power. I have already taken out the battery and waited, put it back the computer; nothing. I switch out ram; Nothing. Switched out the power supply's; Nothing. Only thing I can assume it is would be the processor. Because I have an *AMD APU (Processor + Graphics chip integrated). Is a processor on a pre-built PC replaceable? Or did I waste 400 freaking dollars?? Sorry but this is really getting to me. I REALLY enjoyed having a moderately fast computer.
ANY Help at all would be appreciated!!! Thanks

***By the way the disk drive, hard disk and the CPU fans still run.