Have a Compaq desktop in separate office. Even when I reboot, I have a black screen with a blinking cursor in top left corner. Help!

Suggest you use the Restoration Disk. (CD)
Turn on the computer, put the Restoration Disk in your optical drive's tray.

When asked click on Non-Destructive Restore. (Repair)

If you click on Destructive Restore, (Full Installation), you will wipe out all personal documents you have saved.

For example:
Files in My Pictures, My Videos, My Music, personal documents you have created, and documents you have downloaded.

Non-Destructive Restore, or Repair, will repair the basic Windows files.

If you do not have the Restoration Disk for YOUR computer, you can order it from HP Support. (HP bought out Compaq)

(Your is capitalized, because it has to be the Restoration Disk for a Compaq Presario SR1620NX, and for THAT computer.
Otherwise use a fresh genuine copy of Windows)

In the USA there is no charge for the Restoration Disk.
The shipping and handling is Not free, however.
$17 for a 5 to 7 day ship, $24 for a 2 to 3 day ship.

This is the toll-free number to call in the USA, (24 hours a day, 7 days a week),
1-800-474-6836

http://welcome.hp.com/country/us/en/contact/phone_assist.html

I am not familiar with support overseas, however here is the HP Support page for Worldwide,

http://welcome.hp.com/country/us/en/wwcontact_us.html

Write down the Product Number, and Serial Number from your computer, to give to the nice person on the phone.
You'll find it in the white Service Tag.

The Service Tag will be located on the back of your computer tower, or up on the side.

More info regarding this,

http://h10025.www1.hp.com/ewfrf/wc/document?tmp_renderType=findModel&lc=en&dlc=en&cc=us&docname=c00004461

(Left-click on the + sign next to each heading, to expand it.
Example: Look on the product identification labels)