Serenity, as Fulmar posted it's hard to know what to do with so many people suggesting things. My advice would be Follow the general lines Fulmar and BaldEagl have. Not to say anyone else is bad to listen to, but they seem to be the most knowledgeable of the Tech support around here, next to Skuzzy of course.
As for replacing the PSU, it's not so hard as it looks. I replaced my first PSU back in March and have replaced it 3 times since.
Some simple things to do: Of course have the PC Powered off and unplugged from everything before this.
-Open the case and simply look around inside the case and study it for a bit. Get a good idea what is connected to what. Where Wires go.
-Attempt to find out where the PSU will slide out, visually. See where it is blocked, and obviously will not come out. Figure out if there are multiple ways.
-Take notes if needed for where wires are going, and what is connected to everything. Just see what type of wire goes where.
-If needed test how to remove some of the wires safely. Such as the 20/24-pin Motherboard connection has a clip, while 4-pins simply pull out.
Safety:
-Make sure to be grounded if you decide to touch anything.
-Don't pull on the wires to remove a plug that is in too snug, simply wiggle it out slowly and carefully.
-Don't have food/drink anywhere nearby.
-When removing the PSU be sure not to accidentally drop the screwdriver inside the PC. May sound dumb, but I lost a Motherboard to that.
Of course I am no expert. Simply ask around if you have a problem in that little box.
Please don't take my path, Trial and Error. It cost me 2 Motherboards, 3 PSUs and 2 CPUs over the past year or two.
Also, Fulmar quick question: I have a Micro-ATX form, and use a ATX PSU, should it not fit due to that? (Assuming the Specs are right it's ATX.)
"If it isn't working, don't force it" X