Why does my PC seem slower?

I think that I have hardware problems which is slowing down my PC.

First the specs -

Pentium 4 2.4Ghz
1 Gb RAM in 2 X 512Mb DIMMS
2 80Gb ATA100 HDs
Sony DVD burner
Virtual memory set at 2048Mb FIXED (I did this on recommendation from an article on capturing digital video from camcorder.
Windows XP Home - hard drive recently reformatted and most software reinstalled in an attempt to speed things up

MY PC seems to run slower doing some things, for example after double clicking MY COMPUTER a window opens immediately yet it takes around 3-4 seconds to display all the drives (the window is empty for at least 3 seconds and then everything displays). Also there seems to be a longer delay in launching applications (after double clicking their icon) as well as displaying the contents of a drive after double clicking it's icon).

I am sure my PC used to be a lot faster than it now is and although 3-4 seconds isn't long I'm sure it used to be much faster.

Could my RAM be having problems. Please note that to be best of my knowledge one DIMM is DDR333 (the fastest the motherboard supports) and the other one (purchased in the last 12 months) is a DDR400 as I couldn't source DDR333 at the time. I would have thought that DDR400 is just capable of running faster and so should matter.
ALSO I think (but not sure) one DIMM may be single sided and the other double sided although the motherboard manual has a diagram on how to install a mixture of single and double sided DIMM types.
I guess maybe I should remove one DIMM and see what happens.

Can PCs slow down this way due to hardware problems and if so how cdan I test to find out what the bottled neck is?

 

Thanks for the suggestion. I have now tried that and rebooted with single DDR400 512Mb double sided, then single DDR333 256mb single sided, then dual DDR333 245mb single sided without any noticeable difference.

I have noted also that the delays are not regular (at times the delays are minimal). I am now wondering if there could be some background process running at the same time which is soaking up resources as I experience delays.
What is the best way to determine if anything else is running when I experience delays. I have seen in the past a system monitor and know that Windows installs a performance console by default and that performance logs and alrts are supposed to be avilable but can't remember how to access them.
Please help.

 

I'm not one for mixing memory but if you ran for awhile with your "odd couple" and have since noticed a slowdown compared to its early performance, I'd tackle this from a different front. Download and install CleanUp!. Before you run it, go to options and take the check mark out of delete cookies. Then run this utility and report back. I'll be surprised if you don't notice a difference in speed.

 

Things seem to be a lot faster now thanks.
Since posting I also considered "ad ware" and so ran Ad-Aware which found 1 entry.
"My Computer" now opens almost instantly.