Find your statement. There should be a phone number and/or a website address and call or log in(you'll probably just need your company name and SS#). If you can't find your statement then call your human resources dept. of the company you had the 401k with. Basically, a statemnent--which you should be getting-will provide your balance and the information needed to get current values. Your statement should be mailed to you or given out to you by your employer on at least a quarterly basis.
If you have no idea who the administrator of the fund is, you can always look it up from the http://www.brightscope.com front page, in the white box in the middle right hand side. That should have the contact information you need to get the information. When you check, make sure they have your correct contact information so that you don't find yourself in this situation again in the future!
It is the law that your employer must give you a statement of your account at least quarterly if the olan is "self directed." If it is Trustee directed, they must give you information at least annually. If your employer refuses to give you infomation about your account in the plan then I would suggest that you call the local Department of Labor office and ask to talk to an investigator and then give him what you know and ask for his help. You may find that they will call your employer and motivate him to give you the information you want and are entitled to. Good Luck! Herbie Glass, Certified Pension Consultant