Memory

Windows may not be the problem,check the motherboard manual and see what is the maximum amount of memory it can operate with.

My motherboard does support up to 1 GB memory.

Yes, Windows 9x has a problem working with more than 512MB. Check Microsoft technet, search for article Q253912. Essentially, if you really think you need this much memory, you're going to need to upgrade to NT, 2000, or XP, as the solutions to fix this problem in 9x 'disable' windows use of the memory above 512MB

Although your M/B does support (ie can address 1Gb) and Windows can (sort off) support 1Gb. You will find that one of your cards or peripherals can't address higher than 1Gb and will installing itself into the space downwards of 1Gb.
If you reallywant to run this way (I can't see point myself, use NT), run it in 512Mb do a memory map in msconfig and find what is sitting in the memory just below 1Gb and that will be your problem, upgrade it or dump it.
Hope it helps.

see MSKB Q 304193 :

To work around this issue, add the following line to the [386enh] section of the System.ini file:

MaxPhysPage=40000
This limits the amount of physical RAM that Windows can access to 1 GB. To add this line, use the following steps:
Use any text editor (such as Notepad) to open the System.ini file in the Windows folder.

Add the following line in the [386Enh] section of the file:

MaxPhysPage=40000
Save the file, and then restart your computer.

For additional information about the MaxPhysPage entry, click the article number below to view the article in the Microsoft Knowledge Base:

Q181862 Specifying Amount of RAM Available to Windows Using MaxPhysPage

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