Nearly Brand New Dell Dimension C521 Won't Post - Stumped

Awhile back I found a unused Dell Dimension C521 with Vista along with monitor, keyboard, mouse, cables, speakers at an estate sale. I brought it home, did a clean install, put some apps that still have support, and added some retro video games. I used it for maybe 3 hours. I put it up for sale and I just sold it and the buyer had a request for a game so I went to install it tonight and it won't post.

When I hooked it up, I didn't listen for the post but there was no video output. I changed out VGA cable and then switched to another monitor and then got out the Dell Monitor to see if it would detect it. It says detected but immediately moves into power saver mode and then I realized there was no post. Fan kicks on, lights kick on but nothing. I checked all internal cables, RAM, HDD, and everything is hooked up as it should. This PC has been in the packing styrofoam other than the 3 hours I used it. It hasnt even been connected to the internet.

Any ideas? I am stumped.

 

Check your beep codes. Actually, looks like yours has led lights to troubleshoot.

“When I hooked it up, I didn't listen for the post but there was no video output.”

https://dl.dell.com/manuals/all-products/esuprt_desktop/esuprt_dimension_desktops/dimension-c521_service manual_en-us.pdf#page48

Pages 49 and 50. LED lights should be on the mobo.

 

Thanks, it does beep but it also has LED lights. I got up the next morning, I rechecked everything before trying, and made sure to press into all cables, RAM, etc and it booted right up without any issue. I don't know if a stick of RAM wasn't secure or what. I booted it up about 10 times to ensure no further problems and got it to the UPS store in time to ship it out. Thanks for responding.