Unfortunately you cannot get PSW because you have been on SEGS previously.
245Z. Requirements for leave to remain
To qualify for leave to remain as a Tier 1 (Post-Study Work) Migrant, an applicant must meet the requirements listed below. Subject to paragraph 245ZA(i), if the applicant meets these requirements, leave to remain will be granted. If the applicant does not meet these requirements, the application will be refused.
Requirements:
(a) The applicant must not fall for refusal under the general grounds for refusal, and must not be an illegal entrant.
(b ) The applicant must not previously have been granted entry clearance or leave to remain as a Tier 1 (Post-Study Work) migrant.
(c ) The applicant must have a minimum of 75 points under paragraphs 51 to 58 of Appendix A.
(d) The applicant must have a minimum of 10 points under paragraphs 1 to 3 of Appendix B.
(e) The applicant must have a minimum of 10 points under paragraphs 1 to 2 of Appendix C.
(f) The applicant must have, or have last been granted, entry clearance, leave to enter or leave to remain:
(i) as a Participant in the Fresh Talent: Working in Scotland Scheme,
(ii) as a Participant in the International Graduates Scheme (or its predecessor, the Science and Engineering Graduates Scheme),
(iii) as a Student, provided the applicant has not previously been granted leave in any of the categories referred to in paragraphs (i) and (ii) above,
http://www.ukba.homeoffice.gov.uk/polic ... es/part6a/
You probably should look at other work based routes.