I from Austria and studied in the USA for a while. After graduating I applied for post-completion Optional Practical Training authorization (OPT). However, this is where my problem starts. I had to leave the country right afterwards. I know that this was not a good idea but I had to have surgery in my home country. Besides I had no place to stay in the USA and no money and obviously I was not allowed to work. My OPT application is now being processed. I wonder if can I reenter the USA with an ESTA before I get my EAD card for the OPT?
If you enter the USA on any status other that your F-1 student visa (such as your ESTA), there is a high chance that your SEVIS record and F-1 student status will be terminated. This will prevent you from being able to work on your OPT once it is approved.
The most simple next step is to wait until your OPT is approved and have your university or a trusted friend mail your new EAD to you in Austria. If you are unable to wait in Austria, you should contact the international student center of your school/university to get their advice on entering the US after your program completion date while you are still waiting to receive your EAD.