殘燈無焰影幢幢，

Dying lamp carried almost no flame and the dim lights were flickering; 

此夕聞君謫九江。

now this evening I heard you were relegated and dispatched to Jiujiang.

垂死病中驚坐起，

Dying was I being statled and got up upon the news,

暗風吹雨入寒窗。

while into my cold window the dark wind and rain swept strong.

PS  Again, 樂天 is 白居易.  Remember his famous verses "座中泣者誰最多, 江州司馬青衫濕."?