The icons and the taskbar appear only after around 45-90 seconds after started my PC. Sometimes it exceeds two minutes.

The decreasing performance could be due to many factors - virus, fragmented hard drive, bad sectors on the hard drive platters, too many programs starting up in the background, insufficient space on the primary partition, bloated junk files folder, registry errors, bad or corrupted system files, etc. In order to resolve your issues, you should tackle each of these issues step by step. Run a virus check, scan and repair your hard drive for problems, defragment your hard drive, update your operating system, remove unwanted junk files using a disk scrubbing utility, uninstall programs that you don’t require, remove entries from the startup (MSCONFIG) that start programs automatically, and use a utility to scan, repair and defrag the registry. Apart from these issues, your system can also underperform due to overheating. Open the computer cabinet and clean out the dust using a blower and a brush. Ensure that the processor, power supply and case fans are dust-free. Neatly tie the cables to make sure there is enough air fl ow. Also keep the computer cabinet in an area that has air circulation such as on a desk or away from the wall. If you follow these steps regularly (at least once a week) your system should work fine.

Neatly tied cables can reduce heat by increasing airflow inside the cabinet.