In my opinion, as you are trading in shares the LTCG or STCGH would not be applicable to you.
Once you show your income as share trading income on trades done on line, I feel you can deduct expenes such as for braodband, telephone etc. and also claim depreciation on your PC!!
One may not file IT returns for non taxable income but it good to file a non taxable return to maintain a coninuity of records in the department!!!
Well views of a lay man, do seek guidance from a CA, there must be a few around on the forum.
Look for a thread : Post your tax queries here, or similar titles thread and post your query a bit more detilaed there to get appropriate responce.