There are at least three types of difficulties you may experience on the Gmail login page.
The first of those is the situation where you access the said Gmail login page, only to realize that you have actually forgotten your Gmail login credentials, and you therefore can’t go past the said Gmail login page. Gmail does provide you with a system through which you can go round this problem, but it is quite a bit of work nowadays.
The second of those difficulties would be manifesting where you enter the correct login credentials, only to be told that you can’t access your account because ‘cookies are not enabled’ on your browser. You only need to enable cookies on your browser, to go past this problem. But, in some cases, all it takes is to close the browser, load it again, and trying logging in – and there is a possibility that you wouldn’t get the error this second time round.
The third of those difficulties would be manifesting where in spite of entering the right Gmail login credentials, your browser keeps on returning an inexplicable error message. This could either be on account of Internet connectivity issues, or some sort of a barrier (maybe a firewall) meant to keep you from accessing Gmail.