Not able to get peaks in HPLC

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chetan.gaonkar's picture
Not able to get peaks in HPLC

Hi I am Chetan Gaonkar, I am using a Agilent 1200 series LC system. I used an Zorbax C18 column (4.6x250mm 5micron)for separation of free sugars from water samples using Acetonitrile:Water (85:15) and RI detector. I had created a method for separation of free sugars and analysed few of my samples using the following method.
After my analysis i purged my column using same ACN:Water. After a few month I had to analyse few other samples so I started with the sample analysis, but I was not able to detect any peaks with standard nor samples. 
To solve the problem I
1) Used fresh Standards
2) Prepared fresh Mobile Phase
3) Filtered my samples and increased the concentrations
4) Re-write the completed method 
5) I also tried changing the column to assess if my column had saturated (But it didnt work) 
But Nothing helped
While using the instrument, it showed an errorr (Unbalanced diodes).
I dont know whats wrong, Please do the needfull to solve my problem soon
Thanking you in advance