Talk with your parent if his disability is only physical, and he is still mentally competent. Express your concern over his inability to get around and take care of his own affairs. Offer him the option of allowing you to act for him through a power of attorney. Expect some resistance; no one likes to give up control of his own life and personal business, and he may not be eager to share the details of his financial situation with you.
Suggest that you and your parent draw up the power of attorney together, or, if possible, have him accompany you to an attorney’s office to have one written professionally. Both options will allow him a clear understanding of what he is authorizing you to do. If you choose to write your own document, you can download one from any legal website and discuss each entry and option with him. If you take him to see a lawyer, the lawyer can also help allay any fears or concerns your parent has.
Deliver copies of the completed POA to any entities with whom your parent has authorized you to interact. For banking institutions, make an appointment ahead of time and plan to take your parent with you, if possible. Some banks have their own procedures and formats for POAs, so you may need to have your parent sign additional documents to deal with them. If you’ll be dealing with real estate on your parent’s behalf, file a copy of the POA with the recorder in the county where the property is located.
File a petition for conservatorship or guardianship of your parent, if he refuses to grant you power of attorney to manage his affairs. If you genuinely fear for his ability to do so himself, you'll have to ask the court to intercede. As conservator, you would only take care of his financial affairs. As his guardian, you would also be responsible for details of his daily care.