Check CPU usage
Use Task Manager (Ctrl+Shift+Esc), select the Processes tab and click the CPU column header to sort processes by descending CPU usage. If there is a process (other than "idle") that is using most of your CPU, most of the time, you can stop that process or prevent it from loading at startup.
Anti-Virus
In some cases, anti-virus products can conflict with other software. Microsoft's Security Essentials occasional does so (look for "msmpeng" in task manager). You may be able to observe this using Task Manager. If so you can try temporarily disabling other startup processes one at a time and rebooting until the conflicting program becomes obvious.
Startup programs
Use the Start icon to run or search for "msconfig", this lists startup items and allows you to disable them. This can be useful for identifying programs that cause problems.
Worst case
Backup your data, check you can read all your backups, reinstall Windows, restore data.
@dual operating system?have you checked disk for errors?does your registry defraged?open msconfig from command prompt and check for startupservices,and inetmgr to check current services running in background which cant be viewed in taskmanager – BlueBerry - Vignesh4303 – 2012-08-11T13:05:19.167
Which processor? the Q6400? Q6600? Q6700? Which Browser? IE? Firefox? Chrome? Is it a special 64 bit build of Firefox? What size Hitachi drive? SATA or PATA? How old it is? How many tabs do you have trying to open at once in your browser when you open it? What else do you have running? Do you have any toolbars installed? have you tried another browser? Have you scanned for MALWARE and SPYWARE as they are not covered by most (if not all) Anti-Virus protection? What else is slow? Details... these are the details we need. – Bon Gart – 2012-08-11T13:41:07.980
1which antivirus program you have? sometimes antivirus programs uses too many of resources. If you running windows then use Microsoft Security Essential. – Deb – 2012-08-11T13:50:08.987