Like all other RDBMS software it is not unusual to have problems from time to time, fortunately Informix-IDS suffers significantly less than the other vendors offerings.
The Global Support Site should provide country specific information
Should be obvious really but if you've bought your solution from an ISV or VAR then they should be able to help resolve your problems
There are a number of Informix consultancy capable of helping, some can provide basic troubleshooting, others are capable of bringing downed systems back online. These companies are also able to assist when your product is out-of-support.
The Manuals provides provide an excellent source of information.
The CDI newsgroup dates back to the early 90s and is still probably the best free source of help available. Most questions are answered swiftly and accurately by some of the most respected names in our industry.
The IIUG provide a number of forums that allow users to request help. User registration is required.
Of course you mightn't need help if you've been trained properly. Training is available from a number of companies