Hardware reserved memory - almost half of the available memory?

Update: after a CMOS reset the bios shows 3896 usable, and the windows shows only 2,2 usable. Now I am confused...
Small addition, but may have it's meaning to professionals: although NUM-Lock status is set to alwasy ON in BIOS, it's never ON when I turn on my PC, I always have to turn it on manually. Possibly mobo issue?

Update 2: i checked in msconfig ->boot options -> advanced -> Maximum memory is checked an set to max 4096 mb.
I swapped the two modules form slots A1+B1 to A2 +B2, now the bios shows up 4095 (one MB less than 4096), which is an advancement, and the windows says now only 1GB is reserved, 3GB aviable. I try placing them back to A1B1 see what happens.

Update 3: so after module swappings and CMOS reset the BIOS finally shows up almost all of the avilable memory (4095 MB), but the windows now shows only 3,25 available, 770 MB hardware reserved. This is ridiculous, I can't find any logical explanation. Any ideeas would be greatly appreciated. I read over the same problems found on this forum, but none of them is similar to mine, since I am not overclocking and I changed nothing in hw config since a year, and the OS is 64 bit. Forgot to mention, the power supply is a chinese, bu fairly stable 620 W supply.

Update 4: things are getting complicated. I tried to make a BIOS upgrade, since my bios version is pretty old. Anyways, I dl-ed the newest shit, put it on a flash drive, BUT the BIOS EZ flash utility doesnt recognize my usb device. It sees an A: floppy drive, and a C: CD drive. I never had a floppy drive on this PC ( i dunno, are those things still around ?), and although I have a CD drive, but I dont have a CD to burn the bios on CD, they dont even sell cd-s anymore. Now what?

update 4: Now I'm going to get pissed off. I found the original mobo install cd, so I did a successfull bios update. This lead me to have now 1GB of hardware reserved memory instead of 770 mb like before. WHAT is this, for god's sake?
.. i guess I sound desperate enough now, which is only condimented by the fact that I'm having a monologue with myself on this forum since morning...

Update 5: I dont really know what I done, but seems that I solved it. I went to BIOS ttweaking page, and removed all auto settings, replaced them with manual inputs. Things like core multiplier set from auto to 16, ddr ram voltage set manually to 1.8V, memory timings and voltage set manually to 5-5-5-18. Whith this, i get an astonishing 1,6 MB reserved memory only, wich is good I guess. I noticed some weird things on the BIOS voltage monitor page though: ddr2 voltage is 1,95V instead of 1,80 as it should be. Why? Well anyway, seems that the problem is solved for now, but I'd still like to get some opinions from you, guys. Tanks.

Thanks, Tradesman, I will do that today, although I have the latest BIOS now and the latest chipset drivers. About the ram modules, I had them a whole night under memtest and I get 11 full passes without erors, so I guess they are good. My biggest fear is that the mobo is giving up, which is very possible, since it is old, but also my worst nightmare. reinstalling this PC to his current state would take forever, just the skyrim mods are 120 I'll be back with a status report, I bought some more ram, see how it goes together.

Update: there is nothing newer than I already have on the manufacturer's website, but that page seems hardly neglected, since the newer processors are not even appearing on the supported list (like the Phenom II X4 970)

Ok, today I have raised the core voltage by 1 step to 1,400 V (only available), wich gave me no real change, I still have 1,6 MB hardware reserved memory both in BIOS and windows, just like yesterday - but this is tolerable. I dunno how many memtest I should do more... I'm afraid to raise it more than the stock max, couse that would already be overclocking, and I lack the necessary cooler for that. Tomorrow I will have more to tell, cuz I will try out the new memory modules together with the old ones (same model, but different version, hope that wont be trouble)

Status report: my memory modules have not arrived yet, but either way, raising the core voltage was not an improvement, but contrary: after 2 days of testing, I realized it causes my favourite game, Skyrim, to crash to desktop with no error report every 2-3 minutes. So this is not sustainable for me
It also caused the motherboard to think the CPU running in high overclock mode ( a yellow led lit up on the mobo, meaning HIGH CPU ). So I switched it back to normal, and Skyrim is running stable again. Good news is that I still have all my memory available minus 1,5MB, wich is ok. I'll be back in a couple of days with further test results....

I think the best - and only - solution might be indeed that some hw parts, most likely the mobo, is weakening, so I will mark that as best soltion, but if something new happens I'll be sure to write it down. The original problem seems to be solved for now to some extent at least, but please dont mark it as solved yet, since many new aspects may occur...