Dell Xps 720 PSU issue?

I apologise in advance for the length of this post. About a year ago I began having sound issues in all applications. The sound would randomly go extremely high at random and then the volume would go very low also having popping and static. Have updated all drivers and checked all settings. The main soundbar knob has little to no impact on adjusting the sound (unsure if this has any relation to my current issue).
A few weeks ago I started having an issue where if I power down the pc and try to reboot it it will give me an amber blinking power light and is basically dead. No beep codes and no diagnostic lights. I've found that if I unplug the pc for half an hour or so it will reboot normally and I can go about my business. If I don't wait long enough the pc will either boot normally and immediately go into powersave mode or I again get the amber blinking light. When I do get the pc up and running the only thing out of the ordinary is that my game video stutters or has occasional graphic anomalies (also new). i have updated bios and all my drivers & also plugging into a different power source to no avail. Also if I dont turn off the pc since it Is now unreliable to reboot , If I come back to it after an extended period of time my screen resolution will be totally changed. Of course my pc is just out of warranty and dell wants to send me a new motherboard, new graphics card and a new psu. This comes to a huge amount of $$ I'm pretty tight on I want to make sure I'm not getting taken to the cleaners because of my lack of pc knowledge. Thankyou for any help you can provide.

If I had to guess I would say your power supply is failing. That it resets it self by unplugging it points to that, it can as well create all the other issues you are having.