About summoning Nyoggtha !
Or you are going about the ritual the wrong way ?
If he is one of the Old Ones as I suspect, certain times need to be observed in order to open the gates - particuarly with relevance to those dwelling outside this Universe.
In the case of Nyoggtha, living under the earth, I am not suggesting there is a gate 'per say' holding him back, but he may be restrained in some other way from escape; just as Satan and his demons are held in the prison of Tatarus - it too being a restrainment hold under the earth. All forms of Restraisnt will have a Key, or words of Power, to unlock their binding hold.
I would check with the Elder gods on this first and see what they can tell you - not that they would approve. I would suggest Enki, or Marduk as the most likely to ask.
Another sign to watch for is 'the sword in the sky' which appears when one of the old ones escapes into the earth. The clouds in the sky will form 'a sword' as an omen of death.
Only a strong and competant magician will be able to restrain and hold them back once released. Restraining is much harder than releasing, so you had better understand what you are actually doing on this one.
Realistically - Maybe restraint is not a bad thing, because the little I know of others who have tried to summon the Old Ones, many have met with an unnatural fate OR got no result.