Application delays (loading, "access" delay when using chat txt field)

So, lately, this has been going on, since replacing my dying PSU. Applications have given me a wait time of around a minute or more when I tried to either access the program, or make use of it while it's active. For example, if I want to load Firefox or Pidgin, there might be a wait. If I want to type a message into the chat field of my IM, there's a wait - and then, after the wait, the text appears. If I want to load Task Manager, there's a wait. If I want to shut down XP, there's a wait - longer than the usual wait, in that case.

So, I replaced my PSU, with no difficulties that I can recognize. I also installed the drivers/program for my Planex USB adapter (GW-US54GXS), so that I could partake of XLink Kai. I'd look at my list of programs that activate upon system startup, but I admit to having difficulty in recognizing what should go and what should stay, as far the MS Configuration tool is concerned. I've been thinking of reformatting the computer, but before I do something that drastic, I wanted to consult this board and see if there's a more practical solution.

I'm genuinely concerned about the stability of my system. Is there any tests that I could run that might help determine my next course of action? I would suggest a HijackMe scan-and-post, but I'm not sure if this is the place in which I'd post those results.

I'll be monitoring closely, as I'll be home for the rest of the day.

Did I forget to mention anything that would be useful? I wish I could think of more, honestly.