i think my psu is dead or on its way out but im not sure i will be sitting on my computer then all of a sudden it will switch off like there has been a power cut this happend 6 times yesterday and twice today and me core votage has went from 1.35 volts to 1.175 volts help please

If you have a multimeter check the voltages on the different rails (while under load), they should be within 5% in either direction, if not then you should probably get a new psu.
What where you doing when you get these cut outs and does it happen with the same thing?

btw, what type is it?

tagan 420w and it happens all diffrent times it has just happend now when i tried to open a web page it happend to my wife when she was on m/s word

Full system specs?

I assume you haven't changed anything recently and this problem has just cropped up on it's own?

i upgraded my graphics card from a 6600gt to a 7900gs on 29 dec and upgraded my cpu from a 3700+ to an opteron 175 at the start of jan

yea, that PSU will not be able to handle such a work load. Its straining 420W to the limit if not too much. So get a good 500W PSU and the problems will most likely be gone.

i dont have the money at the min but i also have three fans is it a cold cathode light aswell as the mother board fans running as well do u think it will work better if i disconnect all of them
this is a total list of everything i have it there i know you r going to tell me it is too much 1xcpu fan
5xcase fan
1 cold cathode light
plus the normal2x dvd drive /writer 2x hard drive so on
too much?

That probably wont help much at all. Return all of your overclocks to stock, disconnect any unneeded drives. I would throw the old parts back in, even if you could run it borderline overload its not worth the risk of potentially ruining your new parts.

i have just taken out three fans and the lights ref my cpu voltage which should i belive bios says 1.28 volts ai booster says 1.3 volts and core temp says 1.175 volts

Yeah, unplugging fans won't make much of a difference to the PSU load.
As suggested, reducing any overclocks to stock will make some difference, as will disconnecting any drives which aren't vital.
(Maybe one of the DVD drives?)
That's the least I would do. Swapping the 6600gt back in would help too (if you still have it of course).

It does sound like some PSU protection is kicking in though, as other problems would probably cause hard lock ups rather than cut offs like that.
Removing extra load or swapping back in old components would confirm the situation.

i have had lock ups as well just not as much as it cutting out

If it was the case that the PSU wasn't the component causing the trouble, you would still need to find out through a troubleshooting process.
At the moment, it is what seems most likely, but if you can reduce the load and lock ups still happen, then we can start pointing fingers at other components.

Have you done any of the other steps? (reducing OCs would be the easiest if you have them. You shouldn't even have to open your case).

i have returned my cpu and ram to stock settings i will see what that does

It's dead, Jim. Well, probably. Get a new PSU before it breaks something in your computer.