The issue is only specific with IE. When logging into portal a blank page appears in IE 11 .
CA API Developer Portal 4.2
The issue can be many hence there are list of resolution that may or may not work.
1.Turn the compatibility mode off in IE .
2. Add the portal certificate in trusted root certificates authorities
3. Under Security--> Trusted sites--> custom level --> From what it was by default I changed nothing except User Authentication --> Automatic Logon with current user name and password
4. same as above for Under Security--> local internet --> custom level -> same as above
5. same as above for Under Security--> internet --> custom level -> same as above
6. One more check you can make to understand which IE is compatible for is open ie --> Login --> Blank page appears then click on settings and F12 developer tool Click on Emulation---> the toggle Document mode to IE 11 then 10 and see which one gives you positive result. Page will reload of its own as you change the option. Also set default app settings in windows the select IE 11 edge
If the page loads when changing the default IE to Edge , then change the default page to IE 11.
7. Add portal domain name in trusted site and local intranet sites under security tab.
If none of the above suggestions work then please open the case with Support.