Short Terms sales with cost basis means that both the sales proceeds and cost are reported to the IRS so that they and you have the information (from your 1099-B) to calculate your gain/loss.
Short Term sales with cost basis not reported to the IRS means that they and probably you did not have the cost information listed on your Form 1099-B.
If the cost basis was not reported or you did not enter it in TurboTax (either manually or from your Form 1099-B), then you should go back and revise your return before filing.You are taxed on the difference between your proceeds and the cost basis. So, as of now, you are being taxed on all of your proceeds. If you paid anything for the stock, etc. sold, then you are being over taxed.
If a cost basis is not reported, then you have to come up with one to enter.
First, I would always be as conservative as possible if you follow the recommendations below.
I would try to come up with a date range as close to the actual date acquired as you can (in your case it may be 1995). As long as it is over a year old, it will not make a difference for tax purposes.
Once you have an acquisition date or range, I would go to the Yahoo Finance Historical Stock Price page athttp://finance.yahoo.com/q/hp?s=YHOO.
You can then enter the stock ticker symbol and date range for a list of prices by day. I would use the lowest stock price and day in your range as the date acquired and cost in order to be as conservative as possible.
