Missed mouse clicks are driving me insane

[nonoitall]

Ever since I built this PC last May, it's had a very strange, intermittent problem where it will 'ignore' mouse clicks for a second or two. I can click the mouse and nothing will happen; I can hold the mouse and after a second it will realize the mouse button is down; I can drag the mouse and mid-drag it will realize that the mouse button is down - or mid-drag it will forget that it's down and let go. It doesn't happen all the time, but it seems like it's happening more frequently now than before (or at least I notice it more) and it really complicates simple things like double-clicking, playing games, etc. (My "favorite" scenario so far is when I sit around for five minutes waiting for a web page to load, only to discover the computer has ignored the click I made on a link.) The motion and scrolling of the mouse never get interrupted, only the clicks.

This mouse works fine on other computers and other mice have the same problem on this computer. The problem persists regardless of whether I use the PS/2 or USB ports. I run both Windows and Linux on this machine and the problem is present on both, so I doubt that it's a software problem, but I can't think of what hardware might be causing the problem (the USB port I used on the mouse seems to work fine with any other peripheral, but of course I can't really test the PS/2 port out with anything besides mice). I'm at my wit's end here. Any ideas on how to fix this, or at least what's causing it? (All system specs are below if they are of any use.)

[*:a47184afee]AMD Athlon 64 X2 4200+ CPU
[*:a47184afee]ASUS A8N5X Socket 939 NVIDIA nForce4 MoBo
[*:a47184afee]CORSAIR XMS 2 x 1GB DDR400 RAM
[*:a47184afee]Seagate Barracuda 160GB HD (x2)
[*:a47184afee]NEC ND-3550A 16X DVD±R Burner (x2)
[*:a47184afee]ZALMAN CNPS9500 HS/F
[*:a47184afee]XFX Geforce 7900 GT EXTREME (520MHz) 256MB
[*:a47184afee]Antec LifeStyle SONATA II Piano Black Steel ATX Case/Power Supply

 

[nonoitall]

Okay, thanks! I'll give that a shot tomorrow and let you know how it goes.

 

[nonoitall]

Cleared the CMOS, but the problem persists. Actually, if anything, it's worse. Before, 76/100 clicks registered. Now, only 63/100 do. It's kind of random though, so maybe nothing's changed.

 

[nonoitall]

Bump.

 

[nonoitall]

Which component should I replace first? (Mouse has already been eliminated as cause.)

EDIT: Apparently, this is one of those freak problems that can't possibly happen, but somehow, has. When I get a little cash saved up I'll try getting a new MoBo and see if that does anything.