Logging in to website using VBA, input fields have no ID

Hi everybody,
First of all, I'm kind of a newbie at VBA. I'm trying to log in to a website with a username and password using VBA, but the only pieces of code I know either input information into the fields by using getElementsById and then adjusting the .Value of the input field, or they loop through elements via "getElementsByTagName", but then I'm not sure how to adjust the value and put a username or password in there.

My code is below; you'll probably find the relics of many efforts including copy/paste, etc.

(BTW in case there's any confusion as to why there's no explicit password strings within the code, it's for security reasons, I don't actually want to store the login info anywhere--what I'm aiming for eventually is where I can press a button, a window pops up asking for name and password, and then once I type that in and press enter, the VBA code will just do everything on the website. A little ambitious, especially for a newbie, I know. I'm confident I can get all the other little parts done, and I did get this code working on Gmail, but I'm having trouble with this site in particular. (Knowing me, it's probably something small that I'm missing))

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This is the HTML form:

HTML Code: 

How 'bout it, guys? What am I doing wrong?

Thanks for the speedy reply!
I'm sure there is a way, I just am not familiar with the syntax. would it be something like Set HTMLDoc.Login.USER.Value = "Username"?

As for the pop-up, it would be great to have one that I make within Excel. I've created a window that I can enter data in and all that, but I do not yet know how to have the code store the data that's entered, at least in a way that I can access elsewhere.

Thanks so much for your fast reply, but nothing happens. The webpage pops up, and there aren't any errors, but neither is anything popping into the username field.

I tried your guys' suggestions. I suppose searching for how to use VBA with javascript code would do the trick, as that seems to be what the site is using for its text fields.

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You guys are awesome, I really appreciate the help.

Nothing has worked, I keep getting an error on

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