I changed my password for google mail on a PC now i need to change it on my Mac for google mail, how do i do it.

See:

How do I change my password on EL Capitan mail 9.2

Changing Gmail password in Mail (El Capitan)

none of this is working for me.. i put in the password (via mail or system preferences dialogue) and blank screen is all that ever shows, password isn't saved, and updated password in smtp list doesn't help either.

Have you tried deleting the mail account from the Mac and then recreating the account on the Mac?

nope.. Do i have to delete ALL gmail accounts, then restart and add them back? Currently the "add back" procedure is hanging at the "select the apps you want to use with this account" dialog box. After un-checking all but mail and notes, and click done... the dialog never goes away and all that is left to do is click cancel. - and clicking cancel means it hasn't been added.

You seem to have a problem with OSX. To fix:

- Try resetting the SMC and NVRAM/PRAM

Intel-based Macs: Resetting the System Management Controller (SMC)

https://support.apple.com/en-us/HT201295

About NVRAM and PRAM

https://support.apple.com/en-us/HT204063

- Try starting in Safe Mode

OS X: What is Safe Boot, Safe Mode?

https://support.apple.com/en-us/HT201262

- Boot to Recovery and repair the startup disk

OS X: About OS X Recovery - Apple Support

https://support.apple.com/en-us/HT201314

- If it is repairable reinstall the OSX

How to reinstall OS X on your Mac - Apple Support

https://support.apple.com/en-us/HT204904

- If you do not have a backup use disk utility to restore the internal disk to an external disk so you can try to recover data.

Then format the startup disk and do a fresh install of OSX