I cant log in my modem, SBV5121E.

Modems like that people generally don't log into, Not really anything you can change in it. Its a standard DOCSIS modem w/out a router built in and the MTA side should be locked down anyways.

What were you looking to do? Maybe there is another way I could help. Is that your modem or are you leasing it from your ISP?
 

Oke, so the problem is that my modem shuts down and then the DS light just keeps blinking. I thought I could log in the modem and reset it. It also happens everyday at the exact same time, 22:35. I called my ISP (ziggo) and they told me that they would look into it, but that was 2 weeks ago. Oh well, that is disappointing. I could just buy a new one but im not sure that will fix it. Thanks anyways!
 
You can reset it by unplugging the power, when the modem goes off that means there is usually an issue with the signal going to the mode,. DS is downstream the Other us the upstream.

If it happens at the same time, its one of these following, they have a maintenance window at that time, something turns on at that time, that causes interference, or you don't notice it when it happens at other times. I would call them wen its off, I'm sure your Receive is out of specification for the modem. If trouble calls/service calls are free I would request one. they can use meters to read the RF strength and find the issue.

I was a cable guy for many a years, modems and cable are burned into my brain forever.