Okay!
First of all, you may have used an abrasive head-cleaning tape, & it may have permanently damaged your heads: I notice you didn't give alot of detail as to brand/type or even how long 'more than twenty seconds' was (25 seconds or 24 hrs?)
I would use a demagnetizer to be sure that it wasn't a simple magnetic build-up that was caused by the cleaner (think you can still buy them at Radio Shack). then try it again.
If that doesn't help, then carefully remove the cover (top or bottom of VCR 'box', depending on brand) & visually inspect the heads- these are the 1.5- 3" round chrome 'pulleys'. Look for any discoloration or buildup on the high-chrome (VERY shiny) surface, & use a Q-tip & isopropyl alcohol to scrub.
Be careful NOT to move the angle or position of the heads as they will not play again IF mis-aligned!