Welcome to Just Answer. I am here to help you resolve your tax and finance concerns. Please feel free to ask anytime you need extra help.
The state tax execution could very well be for a return prepared by the state (or even the IRS) due to a lack of filing or it could be that he actually did file and has a balance due.
To proceed you should contact the telephone number listed on the letter. Once you get a real person explain the predicament and ask if the balance due has been calculated based on a non filing or if a return was actually filed. Include in your explanation of the circumstances his mental health issues. This will result is a somewhat more cooperative attitude from the tax agent.
If a return was filed request that a copy be sent to you so that you can make payment arrangements on his behalf. If a return was not filed you should ask how that tax due was determined and request documentation supporting the calculations.
If necessary copies of W-2 forms can be requested from the Social Security Administration (http://www.ssa.gov/) and any other forms of income can be requested from the IRS (http://www.irs.gov/). The difference here is that W-2 information is sent, by the employer(s) to the Social SEcurity Administration and 1099 forms (interest, dividends, etc) are submitted by the payers to the IRS.
You should get a Power of Attorney signed by your son so that you can act on his behalf. You will need one for the IRS and one for the state. They can be obtained at the IRS web site noted above and the Georgia Department of Revenue web site at
www.etax.dor.ga.gov These forms will give the government agencies the ability to deal with you on this. Otherwise they may not speak with you since you are not the person involved.
Once you have all this feel free to return to me if further assistance is needed.