Ungrounded outlets are a safety hazard and are in violation of the building and national wiring codes. They need be made safe immediately.
In homes where all the outlets were installed with a ground, any failure of the ground must be corrected by replacing the failing outlet, or replacing and/or reconnecting the ground wire. In many cases the open ground on one outlet is the result of a disconnected wire at another outlet. A wire disconnected from one outlet will disconnect the ground service from all the outlets down line.
In older homes the original wiring did not have ground wire connected to the outlets. These ungrounded outlets are easily distinguished by their two hole / slot configuration verses the newer grounded type of outlet that has three holes / slots. Ungrounded outlets that have two holes / slots used in a home that was originally wired in this manner and has not been rewired are considered acceptable.
Where the Problem Begins
The problems for the owners of older homes start when grounded type outlets are substituted for the ungrounded type without the necessary rewiring that adds a ground wire to the new three prong grounded type outlet. Grounded type (three hole / slot) outlets may not be substituted for ungrounded outlets unless a ground wire is connected.
An exception to this rule is allowed by the National Electric Code, when the outlet is protected by a ground fault interrupter (GFI or GFCI).
There are two fixes available for those home owners who do not want to rewire the entire house.
The first fix uses Ground Fault Interrupters. There are two types of GFI available, one takes the place of the regular circuit breaker in the load center. The second type that is available takes the place of the standard outlet and replaces it with a special GFI protected outlet. These are commonly used in the kitchens and bathrooms of newer homes. Most people know them for their black and red reset buttons.
The second fix – In many older homes the outlet mounting box was grounded but the outlet was not, if this the case it is possible to use a jumper between the mounting box and the grounding screw on the new grounded type outlet. This type of ground may not be adequate for surge protectors. (see below)
A surge protector plugged into an ungrounded outlet will not operate as the manufacturer intended. When a large surge or spike hits, the surge protector uses the ground wire to take the "hit" away from the protected equipment and send it safely to ground. If the surge or spike is not sent to ground by the surge protector it will destroy the delicate electronics you were trying to protect. The warranty offered by the surge protectors manufacturer offer, is only valid if the surge protector is used in a properly grounded outlet.