I lost 99% of water pressure in my sink and need help?

The water pressure in my kitchen sink has been pretty bad for a long time. I finally decided to do something about it. I took the aerator off and it was somewhat dirt to I let it soak in some solution. I then went under the sink and turned both the hot and cold valves all the way on. This caused the pressure to go down to almost zero (it barely drips). I have tried many times to turn them back and forth and I can only turn them on and get a drip or turn them off and get nothing. Any ideas would be greatly appreciated.