It sounds like you may have a broken motor coupling. This is a common problem that usually occurs through normal wear and tear. Replacement couplers are more resilient and resist breaking much better. If the washer will fill, will not agitate or spin, but will still drain, these are the symptoms of a broken motor coupling. The accompanying noise of the motor engaging and a rattling/grinding sound is also a common symptom. This is a very simple and inexpensive
repair. The following link explains step-by-step how to replace one:http://www.fixya.com/support/r385252-replacing_motor_coupling_whirlpool_top
The part number is included in the link I provided. You can purchase a replacement on line at appliancepartspros.com for about $11.
If you have any questions, please let me know. I hope this helps you.
NOTE: Roper is manufactured by Whirlpool and uses Whirlpool parts, so these instructions will apply.