I have a 486DX2 that keeps giving a Himem.sys error. It's says Himem.sys was not loaded, loading DOS low and stops. I've checked the hard drive and controller card with no luck. Any suggestions?

Well, himem.sys is a program that tries to control your RAM - it is supposed to be loaded in the CONFIG.SYS file. The error you are reporting here indicates that it is NOT being loaded. If you post your CONFIG.SYS file we can take a look at it and suggest some changes. What OS are you running? Why do you think this is hardware related? To be honest, it sounds like a software issue...

I believe it is a hardware problem because I can take the hard drive out and try it in another computer and it works fine. I've also tried changing the RAM. Right now all it has on it is MS-DOS 6.22, because when the error first came up I thought it was an OS problem. The exact error reads:
ERROR: HIMEM.SYS has detected unreliable XMS memory at address 001003A4h.
My Config.sys:

DEVICE=C:\DOS\SETVER.EXE
DEVICE=C:\DOS\HIMEM.SYS
DOS=HIGH

[COMMON]

REM Do not Remove -- CLOAKING.EXE is required by the Norton AntiVirus DOS TSR
DEVICE=C:\NAV\CLOAKING.EXE
[COMMON]
DEVICE=C:\NAV\NAVTSR.EXE

All suggestions appreciated! Thank You.

Ah - you just posted a big part of the error message which you left out of your original post.

The error you are getting almost always means a bad RAM chip or a bad memory socket on the main board. Did you replace all the RAM or just some of it? Is there any onboard RAM?

I replaced all the ram chips. I do not believe it has on board ram. Is the config.sys the only thing that requires himem.sys?

Himem.sys runs a check on RAM, and takes control over it. It then feeds out memory to applications asking for it.

If you take that line out of the CONFIG you will find that many programs won't work correctly.