Hi Neha,
Apologies for the short note, was running between stuffs.
Here, if you were able to open workbench earlier and it has gone down now, you have to check your system's Java advance settings from control panel. If it never turned up, you will have to check if you are using correct JRE version.
Share a screen shot of java setting so that i can comment further.
Best Regards,
Swaroop