Check the basics first: make sure that the batteries are touching the metal contacts and are in the right way around. Check the batteries' power; if they have run out replace these batteries with new ones.
Remove the cassette from your recorder, if there is one, and ensure that there are no obstructive materials in the microcassette tape recorder's main cavity. Make sure there is nothing wrapped around any of the cogs or tape heads.
Dampen a cotton swab with some isopropyl alchohol and gently wipe the tape heads. Repeat this with the other components such as the cogs that the cassette fits over. Dry these parts afterwards with a clean cotton swab.
Take your microcassette recorder to an audio repair store and ask an expert to look at it if none of the above methods fix the recording problem.