My XPS420 seems to have had a failure of some kind - when i power up the fan starts on high, motherboard lights come on orange. power light on psu green, then maybe a second or two later pre bios / pre diagnostic lights, it switches itself off then back on again ad infinatum.
have tried unplugging everything inside - the only thing that seems to make a difference is the CPU - if i remove that then it stays on but i still don't get any diagnostic lights
Welcome to the community
Sounds like there is something wrong on the motherboard. Have you tried connecting the CPU back? You can also try to remove the RAMS and turn it on without it. See if the motherboard beeps. This will determine which causes the problem. Let me know of the results! Glad to help!
motherboard was definitely dead - amazingly my local dell reseller had an identical one in stock, which i've replaced and it works fine.
Anyway its good reseller has some stock, and good to know the computer is functioning now.
Feel free to post back here for any concerns, we are here to help!