You probably had a mail containing a link or some malicious code which has prevented your .exe and .lnk files from working. The first course of action is to download a strong anti-malware programme and scan with it. Go to http://www.malwarebytes.org and download MalwareBytes also known as MBAM. The free one is a trial version and that will be enough. Install it and restart into Safe Mode with Networking by tapping the Function 8 key as the machine powers up and selecting it form the Advanced Boot menu. Update MBAM again and run the full scan. When it completes, click on Show Results and then tick everything (the paid-for version does that for you) and click Remove Selected. Restart again and have a normal startup this time.
If links and progammes still fail, go to http://www.dougknox.com and click on the XP Fixes link on the left hand side then on File Association Fixes in the middle pane. Again in the centre pane, you'll find Doug's EXE file fix - double click that and download it then click on it and allow it to modify your Registry to put this problem right. Go back to the same place and get the fix for LNK files and do the same. After a restart, things should be back to normal.
you may need an antivirus, malware does not usually interfere with system files. download avast or avg, run safe mode by pressing F8 before windows starts. scan, delete/uninstall any unknown programs. reboot
you may need an antivirus, malware does not usually interfere with system files.
I disagree strongly with that as many do - especially if it suits the developer to stop you form opening Task Manager to close the malware, of go into system configuration to prevent the malware from starting at boottime.
Blocking .exe files stop your AV from working and the only exception is IE and the only site you can get to is the one where the malware wants your credit card details - ostensibly to get rid of it. Usually, of course, it doesn't work but it does manage to take the money.