Make sure your contacts are clean. If they have been well kept, I think it's ok to wear them. But if they haven't been used for a long time, there are risks for irritants and bacteria may have built up on them. So clean them thoroughly before you wear, or your eyes will be infected.
Even the contacts has been put in the solution all the time, it is not safe to wear them for the solution may lose its ability to disinfect the contacts. If you have no choice and you have to wear the old contacts, try getting some new solution to wash the contacts. If you don't have fresh solution, you can make some salty water. The salty water can kill most the bacteria, but not all of them and then clean them by distilled water. For safety's sake, you can use some anti-infection drops while wearing old contacts.