Can anyone help me know how to reinstall LR2 which I purchased on my new computer? I no longer have alas the serial#
The phone support I talked to and the chat feature were totally brainless so disappointing
No serial number. Try this: Find your Adobe product serial number quickly
If it's not there, you need to develop a method of keeping track of all of your serial numbers (for all software) so you don't lose them in the future.
With regards to Lightroom, without a serial number, you'd need to purchase the full upgrade to LR 6 at 149 US Dollars; or subscribe to the Photography Plan which includes Lightroom CC 2015 at 9.99 US Dollars per month