I am using windows7(authentic version) but facing problem in booting the system!my system is going slow day by day! The reason may be avg anti virus or probably some other problem which I am not able to trace out! I work on multiple applications at a time so a speedy operation is my most important need! can you suggest ways to improve my speed?

Well. There are some configurations to be done.
First of all, if you want to check for an application (or may be a system error). You have to use the Event Viewer. That is the easiest way to debug the issue. You can launch it using Run box. Type in Eventvwr.msc and hit enter. Check the Application category and then System category.
If you have found NO errors (ignore warnings), you have to configure the AV suite to use Minimal Resources. You have to Disable the Unwanted Components. Each and every AV suite must be configured properly to avoid the Slowness. For AVG config is quite easier than other heavy products such as Bitdefender or Kaspersky. Are you using the Free version or the Full version? Have a doubt on that.

You have to configure your Firewall (if you use the Version which includes a Firewall) to use Medium resources.
You can Disable Anti Spam, Email Scanner and IM protection (located in the Online Shield) if you do not use Personal Mail Clients and well IM protection is not very strong in AVG.
You have to set System Monitoring options to Custom level. Configure it to use Minimal or Medium Resources. - Recommended to use Customized Options
Set scan settings (real time scanning by Resident Shield) to Customized and chose the level you want. Same applies to the Online Shield but I recommend you to keep Optimal settings for your Safety.
If you are not connecting to the Internet its fine to use Game Mode.
Configure the Identity Protection by disabling unwanted options.
Set the Virus Vault to a healthy size.
Link scanner may give you faulty information and restrictions. So use it wisely.
The most important setting is in the "Scans". You will e able to control the Impact on the System Resources.

Finally: Make sure that your System is free of Viruses. Delete the Quarantined Viruses.