I'm wondering if I've blown my lcd by accident. It's supposed to be a 20 * 4 rows lcd however only row 2 and row 4 seem to light up. Should they not all light up
Some four-row LCDs are actually two controllers with separate enable inputs.
Try writing to all the locations in the data RAM, the memory-address to character-location in these LCDs is not always what you think it is. For example I have a weird 16x1 display that is actually laid out as two disjoint 8-column memory ranges.
Check your programming and connections. I doubt that you could damage module in such way that only two rows which aren't close together remain functioning.