Umax astra 5800 driver for windows 7

Go the manufacturer's support website for your country and look there.
If they don't have Win7 driver for it, try the Vista driver.

If all else fails you can install the trial version of VueScan software which supports most USB scanners: http://www.hamrick.com/

If it works with your scanner, buy VueScan or buy a new scanner instead.