Motherboard or power supply (Codegen 300X) issue?

I have an old PC with a booting problem. I'd like opinions on whether the problem is the Codegen 300x power supply or the motherboard itself. I don't want to be fobbed off into buying another machine just yet. The machine shows the following symptoms at boot up:

1. First attempt at boot *on a cold machine*: Boots up then freezes with screen image remaining. It may take 5 minutes to freeze during which time the machine is capable of doing useful work.

2. Second and subsequent attempts at boot on a cold machine after removing and replugging power cord:
EITHER: Boots up (screen LED goes green) then does one of two things:
- a. Hangs with screen image remaining
- b. Cuts out completely - with screen image disappearing
OR: Fails to boot (screen LED never goes green)
- c. Makes several beeping sounds.

3. After about the 8th - 15th attempt at boot (when warmer?):
- d. Boots up correctly. Remains functional with no problems for hours.
- e. The box behind the power cord (CODEGEN 300W Model 300X) makes a bit of a noise.

4. Performance after correct boot: It gives me *no problems at all* for 24-48 hours at least. It can correctly operate Windows Movie Maker and will save movie files from this program which take over 1 hour to complete. There are no internet connectivity problems. It correctly reads and operates external devices such as a Seagate external hard drive, a jetflash, and a camcorder.

5. Initial boot *immediately after shutdown or standby*: Boots correctly and machine remains functional when the boot is performed on a warm machine that has just been shutdown or placed on standby.

6. This CODEGEN box has been making these noises for sometime even when the machine was booting up first time. However it is no longer making the really bad graunching noise it did *prior* to this booting problem becoming apparent.
 
I've had this formally diagnosed as my video card. I'm not entirely convinced this is the only problem but here's hoping.
 
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