Help me in writing sales letter for my midterms

[EnglishEngineer]

Problem:
1. Make a sales letter. As a sales manager of a computer accessories company, sell the latest USB flash drive to student organization presidents of a university. Cite important features of the USB that the students will find very useful.


Here is my work

Dear Sirs:


What if I tell you that some important files from your USB are stolen? You are at school dealing with computer work especially doing proposals in improving your University, doing your thesis related documents, programming a 2000 line code in a notepad, encoding an important speech for elections and many more. You take your usual 1 hour break by eating snacks at the canteen and leaving your things behind in your school’s library especially your important documents stored in a flash drive.


Months have passed and you are preparing to submit your own work. Another day has passed and you realized you got a letter from the school dean for the sole purpose of kicking you out for plagiarism. Your life now is ruined because of that stupid flash drive.


But not if you have the Kingston’s Data Traveler Locker!


With plagiarism and identity theft on the rise, personal security should be a number one priority. Kingston’s Data Traveler Locker provides personal security for your files. Its password protection safeguards even the most sensitive data in case the file is deleted stolen. Your password becomes the only key to access important files that you care about.


Data Traveler Locker supports Windows 7, Windows Vista, Windows XP, and MAC computers. It’s also easy to use and there is no installation process required.


You can have the Data Traveler Locker with only a discount rate of 20%. But you must hurry because this offer is good until February 20.


Call us at 0927 379-51-61 for more information about ordering and credit card number. You can also use our website www kingston com for more information regarding our latest flash drive products.


Yours Truly,

____________
Sales Manager



Please correct the above for any errors
I also need information on the following
1. What are the line spacing in every paragraph? (My book uses 2 spaces per paragraph)
2. Is it okay if i could indent the top and bottom part by 0.8 inches? (w/c i am currently using because page 1 doesn't fit)
3. Is my spacing below Yours truly, correct?
4. Please correct the above for any grammatical errors
5. Any other necessary corrections?
6. Do i need to add a letter heading above the Dear in a sales letter? (address of our company)

usually everytime i pass a letter i always get marked the wrong format
I know a letter is font 12 and times new roman but is there an ultimate format used commonly in business writing>?