windows explorer has encountered a problem and needs to close. we are sorry for the inconvenience.

The probable reason behind this is a virus.
There are many viruses those hijack windows core files and even explorer.exe by injecting malicious code in those files.
I suggest you two things...
1) If you are facing this problem for the first, restore your windows.
(start -- all programs -- accessories -- system tools -- system restore)
2) Use a good antivirus. Install it to your system and do a boot scan.
(I recommend you Quick heal total security 10)

If these solutions doesn't work at all, then reinstall windows (fresh installation).

if you suspect malware, i suggest to run these :
     Spybot :        http://www.download.com/3000-8022-10122137.html
http://housecall.trendmicro.com/                                                               online scan for trojans
http://www.malwarebytes.org/mbam.php                         MBAM
http://www.spychecker.com/program/hijackthis.html                                   download
http://www.hijackthis.de/index.php?langselect=english                                check the log

Do you have eScan antivirus? Is it a trial edition? If so, uninstall it. It is conflicting with Windows. If you want a free antivirus use something like avg or clamwin.

Lee

Thanks for advise I solved problem myself. Thank you very much