xps 8700

The first question, have you checked where its plugged into the AC power to verify there is AC power?  An obvious item, but I have to ask as this was the most overlooked item that our users missed when calling the hardware help desk I use to manage.

If the AC power is OK, unplug the power cord from the AC power for at least 30 seconds.  Then plug back In and see if it will power up.  There is a "crowbar" circuit (basically an electronic circuit breaker) and if had "crowbarred" the power supply will not power on until AC power is removed from the power supply input for about 30 seconds.

I don't see anything specific in the Dell manual but most motherboards have a small LED light that will be lit if the Power Supply is OK and connected to AC power.  The PC can be "off" and the light will still be lit.

Yes the motherboard light is on, just tried leaving the power cord off for about a minute and still no response

I shouldn't have said the power supply is OK if the LED is on.  Just that it has 5VDC.  

Next step is to reseat (unplug then plug back in) the front panel power switch connection to the motherboard. And, if that does not help, reseat the 24 pin power connector.

#18 on the motherboard diagram is listed as the front panel power connection.

https://downloads.dell.com/manuals/all-products/esuprt_desktop/esuprt_xps_desktop/xps-8700_owner%27s%20manual_en-us.pdf

Still nothing, the 24 pin was really tight and in a bad position to move so I didnt wanna mess with it

Still nothing, the 24 pin was connected really tight, and is in a bad position to move so i didnt wanna touch it.

One final thing.  I don't think it will help but something to try.  Remove the CR2032 battery on the motherboard for at least 10 minutes.  Reinstall and see if it will power on.  

Sadly, the power supply can't really be checked.  Only way to check a power supply is replace it with a known good power supply.   Same with the motherboard and/or CPU.

Thus it may be better to take it to a (qualified) repair tech.  It will cost you but they should be able to determine what the problem is and give you the option to repair (or decide on a new PC depending on what is wrong, as this is a 2015 model.  Depending on what is wrong and how much it costs, it may be better to put those $$ toward a new one).

 Front power button does not light up, the power supply test button works fine, LED turns green and and fans spin normally, already tested leaving the cable off and then trying to turn it on again.

Worst thing is that this is like tge third time this happened usually when I leave it alone for a few hours it would start up as usual when I tried later, i'll have someone fix but don't really have the money to buy a new desktop

Just changed the battery, the power button lit up once when I was pressing the power supply unit button, but it just lit up once and never more, it also didnt turn on I waited to see if my monitor would show anything but nothing

True enough, my dell laptop works fine even after 8 years but this desktop gave me headaches since the beggining, so it might be the model but still, hopefully whatever I get(or if this pc decides to start working like it did other times) it will last longer

Just got in contact with dell support and their diagnostic was that the motherboard itself might be the problem, but the option to repair is around 525 dollars so at this point im considering getting a new PC, this one has been riddled with problems since month 1, and most likely my new PC wont be another dell

Too bad on the diagnosis.  

As far as brands, there are "horror stories" about all brands.  You could get whatever brand, including a new Dell and it works great and lasts a long time.  On the other hand you could get whatever brand and its a lemon.

I'm "fighting" Apple right now for a problem with my iPhone 8 Plus.  

Even though it may be a hassle, its worth reseating the 24 pin power connector.  Nothing to lose by trying it.  That power connector is tight on all motherboards so not just something on yours.