Some Network SHARES not accessible

I have an issue that is driving me nuts (short trip). I have some folders on a Win7Pro 64 machine (hardwired to gateway/switch) I want to share with other computers in our house. There are several folders, each containing many files. I do not want to put all files in the same folder.
The other machines trying to access these files are:
1) WinXP desktop (wired to gateway/switch)
2) Win 7 Home 32 laptop (wireless)
3) Win 8.1 Home 32 notebook (wireless)

At one time, all the shares were accessible from all computers. Then I started having (random) issues with some (not ALL) folders not being accessible (got an error saying I wasn't authorized - denied access). Nothing (that I know of) has changed, some folders (one of the folders NEVER works any more, others work sometimes and not other times). I have checked and reset settings many times and can't find the cause. For example, the share that never works anymore has the same share settings/properties as a share that always works.
Any suggestions?
Thanx!
Mike

There are two settings for this one is the share and the other is NTFS the share can be set for everyone's but if the NTFS permissions deny you won't get in. Often if you create or change a folder it makes you owner and changes permissions.

samuria said:

There are two settings for this one is the share and the other is NTFS the share can be set for everyone's but if the NTFS permissions deny you won't get in. Often if you create or change a folder it makes you owner and changes permissions.

Today I was able to access the shares. I had done NOTHING, made no changes to anything. I suspect tomorrow I will not be able to access some shares.
If it is the NTFS thing you mention, should I just right click the folder, click PROPERTIES and make sure it is SHARED? I'm not an I.T. tech although I have worked with computers a good bit since 1990. However, networking was never my strong suite
Thanx.

The security tab on the folder doesn't have a NTFS share you have to set permissions to everyone or specific user. You have to take care user folders are blocked even to admin the simple way is to set accounts on the PC the same as your logged in with on the PC your connecting from as kits details are passed by default. You have to remember anything you share if you get a virus or ransom safe it can use them to attack all PC on the network

The thing that bugs me is the fact that the shares work OK and then they don't, and then they do, etc. Some of them work fine all the time, one in particular doesn't work more than it works. All the files involved are backed up (in triplicate) and contain no sensitive data, are behind a firewall, and some are encrypted - bottom line is I think I am as secure as I can be - even from myself!